Ahh boo-hoo one series
AOT fans are just not that dedicated. Having one season isnt an excuse to jump ship. Remember the [i]Firefly[/i] TV show? [b]One[/b] series that ended in 2003 and people STILL unironically call themselves browncoats. 

And if we want to talk about animu, while nowhere near as popular, Outlaw Star had one season and still a fanbase that has stuck with it.

80% of AOT fans werent fans at all, it was just the hot new show to talk about, but because of its thin plot and terrible pacing people just didnt want to stick with it.

Most TV shows across the board are mediocre, and even the acclaimed ones like Breaking Bad drop in novelty severely on a second viewing. Only True Detective and maybe the Sopranos could be described as modern classics.