The alternative is to build a new huge airport in the middle of nowhere. Not something any carrier does lightly. Needless to say, either AA had to ferry the aircraft over to SNA (an expensive proposition) or cancel the frequency which the aircraft was scheduled to fly x SNA (an expensive proposition). Thus, not taken lightly.

It's all a binary decision. Land vs. no land. Not a policy or customer service issue at all.

Sounds as if AA handled it as well as could have been handled.