I found this out when I tried to show it to my daughters. Apparently the copyright agreements don't cover how to split the proceeds from streaming, so nobody can sell Amazon, Netflix, etc the right to stream it.
But it is on The Pirate Bay...
What a shame that the rights holders are so short sighted. The nostalgia those old tracks would create would surely sell more records. And it's not like anybody is going to be satisfied with replaying the video when they want the song, with the characters talking over the top of it.
It was not even available on dvd for a very long time. So much potential money lost.
It's weird; you can't watch it on demand, but you can virtually DVR it when it is "broadcast" at an arbitrary time.