@blackdog Having thought of every uncompetitive idea at least once in my life, this was a thought I had as well. However:
-Prefiring is killed, especially if randomization is at choke
-New players might be very confused when learning the map due to its key battlegrounds changing each round.
-Many smokes and other nades lineups are rendered impossible due to lack of certainty of cover placement.
I actually enjoy these ideas, but a good rule of thumb is to keep things predictable and controllable by the player. Randomness is very tilting to play with in a competitive environment (think uno).