And now to continue on from my last post,where I said that it seems The Muppet Movie helped determine who the "main cast" is and order of importance and popularity...
After The Great Muppet Caper and The Muppets Go to the Movies, it seems like there was a period where they shortened their core cast. Maybe it was a case of the Muppets not having a weekly TV spot and limited performers so they limited the amount of characters in a production, but The Fantastic Miss Piggy Show and Rocky Mountain Holiday both had very limited Muppet casts, not many minor characters (though Rizzo was part of the gang in both), and certain significant major characters were left out (Dr. Teeth seems to have been left out of all the early 1980s specials).
The Great Muppet Caper's main cast (which I consider all the characters who go out to stop the jewel robbery at the climax plus Miss Piggy) included all of The Muppet Movie's main cast except Sweetums (who was limited to the opening scene) and maybe Camilla (none of the chickens are shown to be her) plus more characters. Some characters who had presence in the screening room scenes, one character who was only in the finale, and a few who were introduced after the movie was released. And then The Muppets Take Manhattan's main cast (whom I consider the intended stars of Manhattan Melodies) is pretty much the main cast of The Muppet Movie but less - everyone but Bunsen, Beaker (who don't get any dialogue), and Sweetums (who doesn't appear at all). There are other characters who have big parts or at least get a good scene (too bad Bunsen and Beaker's big scene was cut), and it's the first Muppet movie to introduce new Muppet characters, but those characters are all separate from the main group (including Rizzo). It's almost like MTM was having a much smaller main cast, like the previous few specials, but still had a big finale with as many characters as possible - the major characters who didn't do anything here, the minor characters,some obscure characters, and of course Sesame Street characters.
And after that, they kinda seemed to be bringing back a lot of more minor characters. The Muppets: A Celebration of 30 Years and A Muppet Family Christmas both prominently had large amount of characters featured. The home video projects had significantly less characters, especially in terms of familiar characters (I let the compilation videos slide because we get clips with a lot of characters), but the two InteractiVision videos gave a bit of prominence to a few characters who normally didn't get that kind of prominence, particularly not in small projects.
Then came The Jim Henson Hour, which brought us a lot of new characters while many classic characters took a backseat. I don't know if I should really use this as an example, but with the Muppets again having a weekly series, they could have showcased more lesser characters more often. Link actually appeared a lot. But the classic main characters was shortened for various reasons (including limited involvement from two of the core performers and Jim's desire to not just do TMS again).
It seems like during the 1980s, they would often put minor characters we know in productions, keeping a lot of obscure ones somewhat within the core Muppet group, but then in the 1990s, it seems like the obscure characters used were often more likely to be ones we wouldn't have really cared that much for, random puppets, recycled characters, puppets from productions that aren't exactly from "The Muppet Show" family of productions. Of course The Muppet Show did the same thing (but before then there wasn't a real established grouping of who The Muppets are, and there hadn't been many regular Muppet shows before), but then by the 1990s Henson would do more shows with new characters and characters from many of those (which Henson retains the rights to) would show up in the Muppet movies, specials, Muppets Tonight, and so on, more often than bringing in background appearances by characters like The Newsman, Pops, Crazy Harry, Marvin Suggs, Droop, and others (and I know some of these did show up in the 1990s, just not that often). If certain obscure classic characters were included in a scene on Muppets Tonight, it kinda felt more like they were just using a puppet that was handy as opposed to "hey, remember this character? He's being used here!" (and maybe that was the case for many minor character appearances on TMS). Around the time of The Muppet Show's 25th anniversary (if not the time between Muppets Tonight's cancellation and Muppets from Space) it seems the company became more aware of the fanbase and started to use more of the kinds of obscure characters we would have really rather seen. Can't really determine if Disney/Muppet Studios had this mindset when they purchased the characters, but by the time of production on 2011's The Muppets, it's clear they've been giving us the characters we want, bringing us more long-unseen minor characters, some of whom were rebuilt and some of whom were actually the original puppets (since then it has been more common to see minor puppets created around 1996, and I have been surprised to learn that certain puppets being used recently/currently were around for a long time).
Going back to how The Muppet Movie seemed to establish who the main characters and order of importance is, I guess it might help that The Muppet Movie seems to be the most popular of the original Jim Henson trilogy with casual fans (though I feel The Muppets Take Manhattan is most popular, title-wise). Who knows if character popularity/prominence would have been different if the movie had, say, Sweetums not get left behind, Bunsen and Beaker introduced sooner, Gonzo introduced later, or maybe even if it showed how Kermit met characters like Lew Zealand, Gladys, or Thog.
And on a similar note, it also seems like the first Sesame Street movie, Follow That Bird, might have helped determine the main Muppet cast of that, though Sesame Street had been around for a much longer time before getting its first movie while The Muppet Show was only on the air for three years before the Muppets got their own movie. But pretty much all of the Muppets with big featured parts in the film have remained part of the main cast. Yeah, some characters may have had periods where they might not have been seen as much on the show but still seemed main (like Ernie, Bert, The Count, even Big Bird, while Telly seems to be around a lot less now), and I'm not sure what to say about Barkley or the Honkers (it seems they show up from time to time, though it's debatable on how major Barkley is in the movie). There's a lot of characters who were major at the time who didn't get much to do in the movie, and many of them either don't appear anymore (and have barely been used for the last decades) or have gone through periods of not being used (seems Prairie Dawn has gone through periods where she's used a lot and then barely used at all, while Herry has recently been recast after a long period of barely being around).