What's interesting is that the "Variety Show" format that the Muppet Show lampoons/mimics was a common thing from vaudeville through the 1970s, but has basically died as a format since I would guess about the mid-80s.

And I hadn't noticed, really. I do miss the old "variety" style holiday specials that Major Celebrities used to do. There have been a couple (ironic?) one-off stabs at revivals, but nothing sustained. (Stephen Colbert did one; so did Lady Gaga and Bill Murray.)