I suspect the choices about destination are pretty careful decisions, coordinated with local authorities at the destination end. Meanwhile, busses in particular are PREVENTED from exiting the highway system in deviation from their planned route.
The evacuation is -very- managed, and that is in part what takes time to accomplish.
It's probably true but they have got to get the remaining people out faster, especially the woman/children/sick/elderly. They should have done those first. Obviously they need a place to bus them to, though, which is ready to handle the influx. Sounds to me like the rest of LA and some other adjoining deep south states are too 'economically challenged' (to put it politely) to handle more people. Thank God that Texas really stepped up to help otherwise who would take them?