I don't mean this in a snarky way at all, because this is odd, and I would also find it very annoying- but have you contacted AA with these same data and asked them why?

They can claim "weather" all they want, but if other similar airlines (UA are certainly not taking any more "risks" than AA) can get it done, they should be able to have some answer as to why they're not. It's going to take more than one email, and I'd even suggest that you request a call from the executive offices about this- it's not something you'll get a simple answer to in email. I've done this with similar, complex issues (rarely, of course) and it has yielded good results.

Cheers.