I think part of the reason a lot of Henson stuff is not on air is that they have a reputation for demanding high license fees. If you're a TV programmer and you can get Happy Days for $250* an episode versus The Muppet Show for $500 you're going to go to decide to go with the Fonz instead of the Foz.
*I have no idea what it costs to license TV shows on cable, I'm just making up numbers here.