American Airlines believes that the number one thing that they can do to make planes arrive on time is to depart on time. So they’ve made it a company priority to the exclusion of most other things to ensure that flights leave exactly on time or even early.
If gate agents don’t bother processing upgrades, let alone coming onboard to move customers up when a first class passenger no shows, that’s acceptable because D0. If seats leave empty with passengers on the standby list that’s ok. If flight attendants don’t have time to offer predeparture beverages in the 30 minutes the flight is boarding that’s fine too.