My guess is AA wants to downgauge service but cannot find another longhaul aircraft in its fleet that can operate to LPB, one of the highest commercial airports in the world. And even with the 752, it has to depart with minimal fuel and fly down to VVI to pick up the full fuel load for the transcontinental flight back to MIA.
Also, keep in mind that the 752s are getting very old.....eventually they will need to be replaced.