In my world a MtB is a disposable bike and as such long term considerations are of less merit than with a road bike. Having said that every frame I build, regardless of the type, uses a threaded BB for the reasons others have already mentioned.

One of the real problems with using press fitted bearings in a bicycle is that of dimensional fit specs not being held very well. The bike making factories/brands don't seem to be able to maintain the tiny tolerance range that pressed in bearings want. Or at least on enough bikes they don't, so creaking BBs have become a frequent topic. Andy