We're still griping about this? Haven't we moved beyond this yet?
This!
This was the main problem with the show: for one thing, unless there's some kind of legality that prevents them from doing so, we can't seem to get Disney to bring in actual Muppet writers to write for the Muppets. It's as if they're afraid to let the Muppets do their own thing, and think they need more mainstream appeal, so instead, they bring in mainstream writers from other mainstream shows, so what we ended up getting was essentially THE BIG MODERN MUPPET OFFICE BANG FAMILY THEORY.
And yes, there's always been adult humor in the Muppets, but it was always sly and sophisticated: it went over the kids heads, but adults got it, so that was something for them without being inappropriate for kids to enjoy . . . there's a difference between subtly and being blatant and in-your-face.