That's exactly the problem. I've always said that a mainstream audience TV show wasn't going to get really good ratings. And it's the fickleness of the mainstream audience that somehow loves seeing someone wearing a Muppet T-shirt, buys a Funko Pop, laughs their butt off at a Family Guy cutscene or a Robot Chicken sketch about Muppets, and maybe even buy a DVD or two they'll never actually watch. But there's no sense of urgency to actually bother to go out to a movie or regularly tune into to a television program. And fan glasses or not, that sucks. I'm not going to say "you're not a true fan unless you see everything they ever did as soon as it comes out," but this is the exact opposite. The "I remember those guys!" punctuated by a flurry of misinformation, wrong character names, and mentally combining Sesame Street characters with Muppet Show ones. Other than a few periods of lulls here and there, the characters never really went away for too long. Sure, they didn't have a TV show or theatrical film for as long as a kid grows up and struggles to pay for college, but they still managed to make TV specials and appearances. There will always be room for viral videos, Christmas specials (because people only love the Muppets around Christmas because of that darn Christmas Carol movie), and TV appearances, and that's sadly what excites the "what are the names of the two guys in the balcony?" audience. Not a new movie or a TV show, or at least just initially.
For years, the MC member Beaker has been saying something that always stuck with me. The hardcore Muppet fan base is both much smaller than most mainstream fandoms (and frankly, it's less disgusting than most fandoms, look at the Ghostbusters fans...eek), and constantly underground. People like the Muppets. When anyone mentions "frog" Kermit's the first thing in their minds, pigs only bring to mind Miss Piggy or Porky Pig, and while Fozzie's down the list after Yogi, he's always one of the bears that would be mentioned when bears are brought up. These characters are iconic, but somehow that fails to translate into a mainstream massive audience. Don't get me wrong, the disconnect baffles all of us. Fans of a franchise will pour into something they know is downright horrible (otherwise, the Star Wars Prequels would have been flops, as would be the Transformers movies) either to see if it really is that bad or to find more things about it to complain about. But mostly because of loyalty. And while the small cluster of fans mostly does that for Muppets (though there really hasn't been that much I'd deem unsalvageable and terrible outside a bad TV appearance or maybe KSY), the mainstream audience is just the "Oh, I remember how Cookie Monster and Gobo Fraggle blew each other up on the Sesame Street Muppet Show" type.
And I wouldn't be surprised if even the at the time bomb film turned cult classic Labyrinth has more hardcore fans than the Muppets. Farscape sure did for some reason.