I agree that AA.com is a terrible experience, but consider the decision to redesign the site from a business perspective: will making it an order of magnitude more usable increase AA's bottom line by more than some other project they are considering (e.g. opening a new destination)?

I don't know the answer to that, but AA is run by business people so I would wager that the answer is "no," otherwise they would be doing it already.

I think there are some intangible benefits to having a more usable website, but those are intrinsically difficult/impossible to measure so they don't factor into the business decisions.

As a designer, I feel your pain, but the unfortunate reality of the situation is that AA is driven by their bottom line and a more usable website probably won't net them the greatest ROI right now.