this movie is so irrelevant i thought the title was about like a profile-pic avatar and i completely forgot about the movie (this is actually true, i wish it was just a joke)
but yeah, i kinda liked the movie as a kid, but i think what might have happened is: the move was like, okay, but relatively forgettable to the general population so lots of people watched it at the cinemas and then like... never bothered again, unlike something like endgame, which was a huge cultural hit. now what might have caused this is a much harder question to answer... i think a lot of the biggest franchises seem to have some of sequel-ization of sorts, that makes people more likely to follow, and become a part of it's culture, such as the mcu, star wars, lord of the rings, harry potter, etc. and avatar didn't really have that? even something like a disney movie, you can clearly recognize the disney-ness of it, so i think it's somewhat rare to find more references to avatar due to it only being one movie and not having as much to draw off of, compared to these other franchises. avatar felt like a standalone thing, and they never really capitalized on it to try to make it a big cultural hit.
so here's another question: why didn't they make an avatar sequel? why didn't they capitalize on the success of the movie by then as opposed to doing it only 13 years later? and it turns out their main problems seems to have been cameron's ambitions, he had already planned out two sequels by 2006, even before the movie came out, but the team wasn't able to feasibly get it done until now, i guess you can read more about it in this wikipedia page:
https://en.wikipedia.org/wiki/Avatar_2#Production, but basically worldbuilding for a movie of this scope takes a lot of work and effort, and i imagine the production of the original avatar also took plenty of time, with them writing a ton of worldbuilding stuff that didn't even make the movie (you can read about it here:
https://james-camerons-avatar.fandom.com/wiki/Avatar_Wiki). so yeah, i imagine between that and the technical stuff, it slowed down the production a ton, and the move didn't really have much of a grip in general culture, so it was just kind of forgotten? maybe the sequels will remedy that, who knows? but yeah, definitely an interesting case.
as for me personally, i really enjoyed the movie as a kid, and i've probably grown bored of it due to how many times i watched it as a kid LOL. but yeah it's still a very nice movie! and i'm very eager for the sequels, the only real qualm i have against it, was how the soundtrack of the original was handled, which is really enfuriating, if you wanna know more about the soundtrack, i'd recommend this video by sideways:
https://james-camerons-avatar.fandom.com/wiki/Avatar_Wiki!