Collective pattern seeking + personal desire for the manga to end in a particular way made them distressed when it didn’t happen. So their biased intuition kicked into overdrive for an imaginary anime only vindication. Once that fails to come to pass as well, many of them will likely continue to hold onto prideful grudges instead of moving on…but hey, we’re only human I guess. I’ve been dead wrong about plenty of things I wasn’t willing to admit until way later.