Avatar is just... generic. $1,000,000,000 worth of CGI, sound effects, recognizable, A-list actors, and aggressive advertising to guarantee a positive return on investment. The Nai've are automatically sympathetic, since they're all basically idealized humans, except blue.
I wonder if Avatar would be as successful if, say, Pandora was filled with aggressive insects, leeches, mosquitoes, and tiny fish that swim up urethra's. And the Nai've were conventionally ugly, storing large proportions of fat for survival during famine, with saggy tits (even on the men), and weird, alien cultures that a white man human would find frightening, and unsettling, and... alien.
Like, maybe the Nai've celebrate ritualistic warfare perform sacrifices, or use other methods to prevent overpopulation. Maybe all the Nai've speak like someone whose diet is mostly cheese and smoking cigarettes. Maybe the Nai've have a class/caste system, or keep slaves. Maybe some have space-gonorrhea, maybe they breed in litters and the parents kill the newborns least likely to succeed.
Maybe some Nai've take psychotropic hallucinogenics, stimulants, or relaxants. Maybe, instead of bipedal mammals that stand between 5-6 feet as adults, the Nai've are giant snakes, or frogs, that lay 100 eggs at a time, but only about 3 of those eggs survive to maturity.
Maybe the movie wouldn't have done so well if Pandora and all it's inhabitants weren't all immediately appealing, on every level, to humans. You know, if they had some of those pesky "faults" or "flaws" or even "differences" that are common in ALL forms of life.
There's never been a "mission" to these movies, either. it's never been about saving the earth, respecting nature, spreading awareness about pollution or global warming, or protecting endangered species/cultures. "Carbon offsets" are a joke.
"Look, James Cameron deserves a square 800 feet of property (at one location, also some several smaller vacation homes), he's EARNED it! And like the philanthropist he is, he's donated money to a company that does nothing but assure you he really super cares about the environment. Just look at all this wildlife he's saving by hiring us to promote this movie and bolster his public image!"
Avatar 2 might as well be called "check out these sexy 3D models and cool action scenes we made with computers: the movie: part 2."