Firefly is so beloved because people think Joss Whedon is good for some reason. But even still there's quite the difference between a shitty cult sci fi show and a shit anime show. Anime fandoms don't really have catchy names as beacons other than people going around calling someone Narutards or whatever; there's no browncoat version of an AoT fan. The Firefly fandom is a fandom built out of a desire for what will never happen and they don't do much other than re-watch the show and continue posting in their small circle. I have no doubt that there's still a community of people that care about AoT for some reason - hell they just released a boring game to give the fans something to do - but the series is in hibernation and anime weebs don't have the same 'single show' mentality. Nor do a lot of western cartoons, really. Just try and find the overlap between MLP fans and like Steven Universe fans and as one shrank in popularity the other did rise. 

And even still, people can be fans of something without 'sticking with it'. 

DBZ still has fans but DBZ finally has new content and just had to survive on crappy games telling the same stories. Less vocal doesn't mean not there. But while there are probably some AoT fans out there, the name of the weeb game these days is just flash in the pan shows every season. 

True Detective though...ehhhhhhhh. One acclaimed season does not a legacy create. Having recently watched Breaking Bad for the first time, that show doesn't even stay consistent in quality throughout. I wouldn't say that television shows across the board are mediocre, but there's a certain...water cooler-ness quality to shows that doesn't always mesh well.