really i think the reason the onceler fandom was so bizarre was because it represented the ultimate conclusion of very proto typical fandom behaviour in a context that was absolutely not able to handle it and it demonstrates itself most effectively with the way oncest happened
because if you check the patterns you’ll see that the immediate characters and ships that everyone gravitates towards in any fandom are the most conventionally attractive guys that tend to be at the center of the work (but occasionally slightly off to the side); sam/dean in supernatural, john/sherlock in sherlock, john/karkat (arguably john/dave? its been a while) in homestuck, ishimaru/mondo in dr1 and hinata/komaeda in dr2, there’s one for teen wolf but i don’t know enough about it to remember what it was
basically that tends to be the pattern for it, but the problem with the lorax is that there was really only one character that fit that mold: the young onceler. who else is there? the lorax? that kid who’s the central character of the framing device for the film? o’hare? tree girl? all you have is this one guy
so in a furious attempt to create something out of nothing, oncest was born; the idea of shipping the young, innocent onceler shown in the films early sequences with his slightly older, (but still “pretty”) more evil self that is portrayed in the “how bad can i be” number (i believe this iteration was referred to as greedler).
but what about the people who don’t like that dynamic? what is there for them? just one guy again. so it began spiralling out of control, AUs upon AUs spawned for the million possible variations of one character, and shipping them with the original, and then shipping them with each other and ignoring the original, and then creating alternate versions of those that are so wildly different from the original canon that they might as well be something else entirely, and it just became this huge ouroboros of a fandom desperately trying to justify its own existence that was inevitably doomed to basically eat itself
its not so much that the onceler fandom is weird, but that fandom in general has bizarre behaviours and it took this one shitty animated film to really demonstrate that maybe we need to chill