But let's not forget that those characters stood the test of time. While Telly is the elder statesman of the group (he was around since the 80's) and Elmo is a close second, Zoe, Baby Bear and Rosita came out of the turbulent time when a certain purple yutz was stealing the show's spotlight... not to mention multiple important people behind the show passing on in the early 90's.... the show struggled to find itself... and while those three characters are still around, let's remember all those other characters they tried to add to fill out the cast...
Sherri Netherland
Humphry
Ingrid
Baby Natasha
Stinky the Stinkweed
Benny Rabbit
The Clubhouse Monsters
Lulu
Elizabeth and Little Murray Sparkles
And so on and so forth.
While some of them were around until just recently, they all came from having to create newer characters to fill up huge gaps left by Jim and Richard's passing, and Frank's film career. Dave Golez even had to be brought in for a couple episodes.
And most of the characters the fans want need to be recast, and just haven't been yet. Guy Smiley made his first new appearance in the show in nearly 20 years this past season. Recasting muppeteers is easier said than done, as they have to sound approximately like them, and get the characters down right. Look how many people had a hand in Scooter (pun intended of course) before he was finally solidly cast.