I can think of several reasons why. but the main one is that customers expect and deserve a fresh product, not week old leftovers. aside from the fact that you would be spending more money on vacuum sealing bags, time portioning it all and labor.
if you were to go to a bbq joint and had the option of 1. Fresh sliced juicy brisket right in front of you, or 2. The option of ordering week old leftovers, or 3. Frozen and rehydrated brisket, which would you choose?
Meadow Creek TS250, Horizon 20" Classic Backyard Smoker, old style weber performer