Usually it's a rights issue, and often it's music rights. A lot of 80s shows like Magnum (and Miami Vice) used current hit music back in the day that needs the rights renegotiated to air it again. The disc might have gotten it hammered out, but the streams are a separate negotiation.
I've seen that happen with TV shows in syndication. The channel doesn't want to pay for the rights to air a show that used a Stevie Wonder song or something, so they skip over that episode.
Don't believe everything on the Interwebz! A duck's quack DOES echo!