Your experience isn't the norm. I have been staying at Marriott's since the early '90s and can probably count on one hand the times I've had trouble getting the room/bedtype that I reserved.

What probably happened was that someone at the hotel tried to "upgrade" you to a Concierge Level room. There were probably no King rooms available, so they gave you a two Queen room instead. That is probably why you were moved off the Concierge Level to get your King room.