I suppose if you consider Eywa to be a actual god instead of something the na'vi invented then they simply are under it's protection and doesn't need/get to advance technologically because it would hurt the balance of Pandora. This is pretty grim in a way since it means the na'vi are neutered and unable to fullfill their true potential.
The other alternative is that they simply don't have good enough requirements to build a human-like civilization and instead fully embrace what they got, even being able to ride the wild-life using their queue. This could also mean there are more advanced na'vi civilizations on other parts of Pandora and the humans just happened to land in the pandoran equivalent to the amazon or interior Africa
I'm tending more for the former, since the na'vi are very different from every other pandoran animal which would imply that they are genetically modified. Perhaps not by a god, but for such a spiritual and low-tech people a planet-sized AI or hive mind can easily be confused for a god. And such a being could also easily keep the na'vi in a leash so they don't accidentally destroy it while also making sure the have everything they need as long as they do as they're told.>>1776821
Neytiri a cute! She has a perfect body! But asari is fine too