Someone on Reddit emailed Brian Znotins (AA's SVP of Network Planning) about this a few months ago and he replied with the following:

"We generally don’t prioritize a widebody on MIALAX. Our widebodies are really meant for long-haul (trans-oceanic) travel, and only when we have surplus time on them they will end-up on MIALAX.

You probably aren’t too interested in the financial reason for this, but if you are, the short explanation is that it’s really difficult for us to monetize the flat beds in the business class cabin on domestic routes. A flat bad consumes about 4x the space of a coach seat, so we generally need to get 4x the fare on those seats vs coach to make the widebody work. We can do that on long-haul flying, but domestically, we’re lucky to get 2x. So a widebody almost always loses money for us domestically.

I do understand that there’s a bigger picture here about overall loyalty and it’s not lost on me. So feedback like yours helps to keep that in mind as we build our schedules.

While I wish I had better news for you, for now we don’t have plans to put a widebody on the route. But it could appear anyway as we work through our schedule builds and see if there’s any available time left over for us to fit a round-trip or two in!"

Source: https://www.reddit.com/r/americanair...eyre_removing/