Prolly because its about the same price, I know, I know...
You are looking at two different size drivers, yeah, there is a huge 13" sub fad right now, thanks to the good people at SVS and JL Audio.
The thing is a 13" sub has a MUCH smaller SD than a 15" driver, a 13"er will have about 550cm^2, a 15" driver will have 800-850cm^2. So, lets look at how these guys perform, but first, a little about displacement. The displacement of your sexy new 13" driver is 3.2Liters, the displacement of the TC2000 15" is about 4.4Liters, do you think the TC2k has just a bit of an upper hand here?
You might as well compare the TC2000 to the Soundsplinter RL-p18. One other issue I have with that sexy little 13"er, did you notice its sensitivity? Man, its gonna take a whole lotta watts to make up for that, especially seeing how the TC2k does 5dB more output with a given watt than the ED driver, not to mention that TC2k probably handles every bit as much or more power than the 13av.2
I am not even going to bother to enter the parameters right now, I can tell you right off the bat that TC2k is a much more formidable driver, the only advantage that the 13av.2 has is that it is smaller, thats it. Now for a car system that may be just what you need, but for a home system when you have the room for a full 15" driver, there is just no sense in spending so much money on that small of a driver.