Whenever I check out the American Airlines fleet and subtypes (https://www.planespotters.net/airline/American-Airlines), I almost always get a headache just thinking about the logistics of handling such a diverse fleet.

As a server administrator, I know how much overhead this kind of complexity of the operation costs, while the increased profitability of having "the exact right tool for the job" is usually only marginal vs. 'adequate tool for the job'.

LCC's like Ryanair and Southwest know what they're doing with their single-type operations.

American will want to standardize and simplify their fleet line-up too.