To me, that isn't necessarily the case. It seems like they're putting more focus on the younger members like Leela, Chris, and Mando, since they could probably identify with the increasingly younger viewers, and vice-versa. Over the past four to five years, Bob and Susan have slowly been getting phased out, each appearing in maybe two episodes per year at maximum. Maria has also retired after 44 years on SS. The only mainstays from previous years are Luis (1971-present), Gordon (1974-present), Gina (1987-present), and Alan (1998-present).
While we're on this track, I'm not sure what to think of this new focus on the "core six" characters. It's great that Cookie Monster and Grover have gotten renewed recognition after being in the background for most of the '80s and early '90s. Also, Caroll's characters are essential...you can't have SS without Big Bird and Oscar. Elmo and (ok, fine) Abby Cadabby are pretty key to the show as well, especially for the viewers ages 2-4. But what does this mean for other Muppets? Martin Robinson has been a core puppeteer for thirty-five years...it would be a shame if Snuffy and Telly gradually disappeared, unless they were to be recast within the next couple of years (Marty's reached the big 6-0, I believe). Same for original characters like Bert, Ernie, and the Count. I'd hate to see them getting the axe in favor of Abby, Elmo, and the gaggle of one-shot fairy tale characters.
One final thought: I wonder how the show will change with Joey Mazzarino's departure. While I was never liked how he used that one high-pitched voice over and over again, I admit that he's written some good stuff for the show.