In certain states, serving alcoholic PDBs on the ground requires a state liquor license (inflight alcohol does not, whether overflying or O&D). My guess is that perhaps AA has decided not to renew its liquor license in MO and the other states where alcohol will not be served on the ground as a cost-cutting measure. Similarly, USAir allowed its licenses to lapse in quite a few states (including Florida), leading to angry threads complaining about the absence of alcoholic PDBs in those states. With the pulldown of the STL hub, it probably makes sense.