Too bad.
Unobtanium is essential to human space travel, without which our civilisation is in serious trouble. That aside, the Na'vi have something we want, they won't deal, and they are primitive. Law of empires comes into effect here, which is default geopolitics alas.
If the Na'vi were smart, they'd have traded unobtanium for technology and other such things so they could catch up and add more cards to their bargaining hand. Also, compliance and respect could somewhat put them in a "friend of Rome" scenario where they are mostly left to their own devices. Some tribes probably did that with the RDA, mind you, and shook their heads in disbelief at Omaticaya pride and stubbornness ("guys, they can rain death from the sky, let's not piss them off").