Super lame! I've run into the same issue at LAX and PHL.
Apparently, if you take the escalator to the left of the ticketing counters at LAX, there is a Priority Line there along with the PreCheck line.
It's totally insane to me that AA has no Priority lines in airports like LAX and PHL where it really matters, but they do have them at smaller stations like RNO.
I tweeted to them about it and got a canned response.