Board Thread:General Discussion/@comment-60.240.40.166-20140702043848/@comment-3146930-20140702234813

From what we see of the opening narration, humans were still relatively young when the Grimm began to try and kill them. Even if some of them had the ability to use Aura even at the beginning of the war with them, they wouldn't be able to teach people how to use it during the time of war. Dust was something that everyone could use and it was useful because of that reason, being able to drive the Grimm back and allowing humans time to rest and advance.

This was probably when people began to actually learn to use their Aura. Combat schools began to spring up and teach people how to defend themselves against the Grimm. This would also be the time when weapons started to jump in technology as well, meaning people no longer needed to rely completely on Dust and could instead use small amounts of Dust for bullets or rockets. Basically, they compensated large Dust and low tech for advanced tech and little Dust.

As far as unlocking Aura, I'm sure not everyone needs it to be unlocked in the way Jaune had his. Pyrrha mentions that with training, people can learn to use their Aura. Most likely, people can learn to unlock their Aura on their own after enough time and training. Pyrrha unlocked Jaune's as kind of a jump start, as without any Aura to protect him, he may have died in that forest.