Just because OALs have catering capabilities at a given station doesn't mean AA does. If a station has a single flight with catering needs (ie a marginal route MCI-MIA-which operates less than daily as is) it doesn't necessitate the expenses associated with catering capabilities for AA flights.

UA, US and WN are the only US-based carriers that have catering operations in-house. UA has Chelsea (as a hold over from CO), US has catering employee classification is hubs and several large East stations (although food preparation is sourced through Gate Gourmet/LSG/etc, US employees simply load it on the aircraft) and WN has about 20 odd stations domestically with provisioning capabilities where they stock galleys with beverages, snacks, supplies, etc.