Many of my fandoms tend to have "burn-out" periods, or at least a "period spike" where I'm a lot more interested/thinking about it more than usual. Some fandoms that I tend to have periods of really wanting to concentrate on (watcch, listen, play, think about, talk about, look up online) include Looney Tunes, Weird Al Yankovic, Darkwing Duck, Mario, Peanuts, Bob Newhart (with most of the focus being on his show Newhart), old school Nickdelodeon and Nick at Nite, Ernest P. Worrell, Garfield, Calvin and Hobbes, Teenage Mutant Ninja Turtles, SCTV, Saturday Night Live (usually the first five seasons, but more frequently in the past few years loads of other seasons as well), The Nostalgia Critic, and others.
And there'll be things I was a big fan of in the past that I hardly cared about for many years that would suddenly get a big spike of attention from me, sometimes temporary, sometimes lasting again. Just a few months ago, right at the end of Halloween, I was suddenly back into Goosebumps, though after a few months that interest has drowned from my head a bit,though I'm still thinking about it a little. Maybe it will continue to have "burnouts" and "spikes", or maybe I'll care less for a long time. For years I hadn;t watched The Wonder Years, or cared as much about it as I did when it was on Nick at Nite, but after getting a Netflix account I've watched every episode, watched many of the same episodes many times, have gotten a big "fandom spike" over The Wonder Years.
Sometimes, having a sudden bigger interest might come from me suddenly reading about it online (wikipedia and TV Tropes are big contributors there). Or maybe I've been reminded of it via The Nostalgia Critic, The Angry Video Game Nerd, The Rowdy Reviewer, and other online video critics (and the irony is that they were badmouthing those works, or at least related works). And sometimes it might be because there's something new, or maybe a new means of watching old stuff.
My Muppet and Sesame Street fandom is the most present. Sometimes I might go through periods of caring less than usual, but even then, I still go on all the major Muppet fan sites every day, though there might be periods where I'm posting less here and editing less at Muppet Wiki (but so far since sending articles to The Muppet Mindset I have not gone a whole month without doing so). Sometimes I'll be thinking a lot more about a certain Muppet production, product, or character a lot more than others. Other things from The Jim Henson Company are more likely to get more "fandom burnout" from me from time to time. Often I'll care a lot about Dinosaurs, but at times I might be really into Labyrinth, The Storyteller, Sam and Friends, Land of Gorch, Jim Henson's experimental films, and others.
Of course, with Muppets and Sesame Street, the burnout is more over which one I care more about. The Muppets might get more attention from me if there's a new movie or special or video release or something, and Sesame Street might get more from me if there's a video release I'm really excited about, or if certain rare clips are made available. There's only been a few periods in my life where I truly experienced Muppet "burnout", mainly because there were a lot more things that I was suddenly more into.