That's the Fleeting Demographic rule. Kids don't know or care much for characters that aren't on often, unlike us who grew up with them. On the one hand, it is pretty sad that kids don't have the same connection, but they have their own characters they connect to. We've seen Hooper's store change hands multiple times. This next generation will only know it from Alan and Chris. And that's pretty stable considering how many hands it changed in the 90's.
Other than the short lived Twiddlebug revamp and Abby's Flying School (which is no different from Ernie and Bert claymation segments), we're not going to see that any time soon. Sesame Workshop knows that, while Sesame would have been a good children's show anyway, it wouldn't have lasted 5 years, let alone 40 without the Muppets. Even though Jim is erroneously credited with the series, and often times was given a lot more credit than he really did, he did shape the show. Out of respect, SW is keeping the Muppets as Muppets (except for special occasions, like Elmo's Alphabet Challenge). Heck, Disney gave them the distinct honor of letting them still call the characters Muppets. Henson didn't even get that privilege.