You can blame Mr. Hoffman for this one!
Think of it from the manufacturer's view--high efficiency = high cost. Hoffman's Iron Law basically states, you can get low (bass) you can get little (box size) or you can get loud (efficiency) choose two and lose the third.
High efficiency is not hard, mysterious or impossible to do but there are rules. The easiest to think about is bass drivers. To make a driver efficient, it is all about the weight that must be moved. If you make a cone very light weight, it is not only expensive but might lack the stiffness required to hold up as the stroke increases. Now think of the voice coil, that is a moving part so one way to cut weight is to make a shorter coil and make it smaller in diameter--that does work well but limits deep bass ability or how much air it can move. PA woofers are very, very high in efficiency due to a short coil, lighter surround/spider since it don't have to stroke as far and the cone can be lighter--winner as far as efficient but limited total air movement. For this reason, a professional 15/18 or 21 inch woofer struggles with below 30Hz.
To get the deep bass, just make the coil longer, make the suspension surround deeper and the spider larger in diameter with a much longer stroke. Oh yeah, make the cone heavier/stiffer to push that kind of air volume. The down side is it is very inefficient so you had better have higher power handling...by making the voice coil larger. Larger voice coil requires a larger spider to allow the stroke so that increases weight again. With all that weight, you need a hell of a strong motor to move it so time for some monster magnet love which might rock the long/heavy voice coil so... throw in another spider to keep it stable (more weight!) and your efficiency goes down the toilet. A good example of this is a 15" PA woofer at 98dB at one watt and a Tymphany 15" subwoofer at 83dB one watt. Play a 60Hz kick drum through the PA woofer at 120dB at one meter and it takes 160 watts...the Tymphany would require around 5,000 watts to do the same thing.
However, if you attempted to play 20Hz through a professional 15 you'd make a rice hat out of the cone.
The other factor, a HUGE factor for consumers and manufacturing costs is size/weight of the box. Hoffman and his law again, can get low bass, small box and high efficiency at the same time. If you want all three, the box will be very, very large which won't be a sexy, slim piano black tower in the living room. Think a freezer sized front loaded horn which is not pretty, not light, not cheap and can't be mailed easily. This would explain why you don't see such designs at your local audio shoppe'.
Moving to midrange--the same rules apply. You might have noticed that larger mids have higher efficiency...because they have a much larger surface area, which is easier to move air. Very light weight cones, light weight coil assemblies and so on is how to do it. They don't have to be huge, you can get a 6.5 inch closed back midrange that can do 400 Hz to 2KHz easy enough and it belts out 98dB at one watt. Not a problem except... you have to have bass with that efficiency or greater and there goes that huge/heavy box again.
Tweeters---now things get interesting. The common dome tweeter generally can't handle a lot of power, are not that great in efficiency although you can get them at around 95dB max at one watt if you use a waveguide (horn) that really helps. The issue is they can't handle a lot of power because their voice coils are very small. Ribbons are getting better, they are rolling out high efficiency designs that can tap 99dB at one watt when mounted in a waveguide. Downside? Power handling! Peavey made some line array boxes with horn loaded ribbons--getting closer!
That brings up compression drivers, the true ultra high efficiency kings. It is common to see them rated at 107 to 114dB at one watt.
Throw in the beasts have large voice coils and pounds of magnets backing them up--they can take some serious power and abuse without letting the magic smoke out. This is the reason you see them used in PA systems, concert speakers, movie theaters, emergency warning systems and everything else. I saw a BMS driver that could go over 140dB at one meter.
Issues with compression drivers? Oh yeah! They have to use the proper horn to load them correctly and require care to get accurate frequency response out of them. The horn must be specified for the correct dispersion for it's use and so on. This costs MONEY to do right and some horns are over 2 feet wide, costly to make and some compression drivers easily hit 300 to over 1,000 bucks each...then add the horn and so on. Horns are large again...notice the theme? Yeah, big parts equal big boxes and that means weight, huge shipping/warehousing costs and the costs pile up rapidly.
Now lets think about going the other direction. Low efficiency speakers, they can be very small, go deep in bass and since they are limited in maximum SPL, you can use vastly smaller and less expensive dome tweeters, smaller mids and everything else. Think of the savings when shipping this stuff around the world, think of the savings in packaging, damage claims, finishing, veneer costs and small grills. You can get the same performance with a 2 cubic foot speaker as you can with a 20 cubic foot speaker--the only thing you give up is efficiency.
Back in the day, you had low power tube amps--you HAD to use high efficiency speakers to get any realistic SPL out of them. I've seen 12" full range drivers with tiny magnets on them with a power rating of 5 watts RMS. Those things were made in the early 50's when 5 watts is generally what you played with. My buddy has a pair of 1964 Frazier Dixielanders with a 10" folded horn loaded woofer and horn tweeter--it was designed for a band PA speaker. It handled a staggering... 30 watts RMS but it's efficiency was 103dB at one watt. I rebuilt the things for him, changed the wimpy crossover to protect the horn driver so it could handle more power without distortion. That thing would peal the enamal off your teeth from AVR power.
There is still a huge demand for high efficiency speakers, they are used in pro sound, arena sound and movie theaters around the world. For home use, amp power is cheap... laughably cheap so why not produce smaller speakers that waste more power than an oil well fire? Sure, the sound system at the 1939 Worlds Fair used four speakers with four 500 watt tube channels to power them--for a crowd of 100,000 people. Now you can get that level of power to drive an inefficient subwoofer.
High efficiency speakers did not go away because of performance issues, they went away because of cheap amplifier power. You didn't need a Klipschorn taking over the entire living room to hear orchestral music any more. Just as the transistor allowed the audio boom in the early to mid 60's, it also allowed getting rid of giant speakers at the same time. My older brothers purchased their first receiver, it was 25 watts of pure Pioneer silver faced muscle complete with big speakers. Now you can get four times the power at a fraction of the cost so more power equals smaller, lighter, cheaper, easier to deal with speakers.
Say you want high efficiency speakers for use with tube amplifiers, you want THX reference levels with an efficient and easy to use AVR (wife wants ONE box!) or you want realistic levels of dynamics like you are at the orchestra. This is a problem if you want off the shelf speakers with nice veneered boxes that will match your furniture. To do this, look to the home theater brands that build such speakers. Brands like Funk Audio, Seaton Sound, JTR and others. To get to THX reference levels at 16 feet in your basement requires high efficiency speakers so that is available if you know where to look. They are not inexpensive, they are not small and they are not light weight because of Mr. Hoffman and his little rule he penned in 1957. But you can get such things that look decent for the home.
The tube guys that build their own tube amps also build their own high efficiency speakers. They have a high efficiency forum where they do just that. Their creations are works of art, works of blood, sweat and tears...mixed with a little insanity. You have to dedicate a room of your house to use those monsters... but they know what drivers, waveguides, folded horn, transmission line and back loaded horns work for low wattage with clean SPL.
Personally, I prefer higher efficiency speakers--sure, they are larger, heavier, more expensive and tend to annoy my wife but I've used speakers rated at 92dB at one watt or higher for decades...she is used to it by now. At least my 4 foot tall, 157 pound 103dB speakers are gone...I'm sane now with 20"H X 12.5"W X 13"D "big bookshelves" at "only" 98dB one watt. Granted, I have subwoofers driven by a PA amp to keep up with them. The 6 foot tall 2 foot wide X 2 foot deep tapped horns was where she drew the line. Time to build more "end tables".
My HT maxes out at around 110dB peaks at my listening position, not bad for an AVR! My real man system is in the garage, a pair of line arrays and subs that measure at 116dB peaks at 11 feet and 111dB peaks at 24 feet. They are very efficient at around 97dB one watt but line arrays are weird little beasts...and you won't see them at the audio shoppe' either. It takes a special kind of stupid to build such things--and I'm that stupid.
In summation, the reason high efficiency went away was the high cost of tube amps was replaced with low cost solid state. Since size = high costs for the manufacturer, it was in their best interest to get rid of high efficiency speakers. If you want such things, you can get them but not at the audio shop... other people build them which is much easier now with computer modeling programs, horn building programs, crossover building programs, cheap, very accurate measuring gear and scads of information available globally at your finger tips. Throw in major advancements with professional drivers with beryllium, neodymium, carbon fiber and all the advanced adhesives to machining and the pro drivers are staggeringly good.
Enjoy the search for high efficiency on the dark side...