In short to get the job done in a over crowded ATC system. I think the guy who insists on blocking the airwaves with textbook perfect AIM phraseology during a bank arrival at O'hare would probably be on penalty vectors until after the bank.

The readback/hearback system works pretty well, and hats off to controllers who catch missed required read backs with 100% accuracy (though it doesn't happen that often that I hear).

I've always viewed verbal shortcuts as a courtesy to other aircraft and the controller who's doing the best they can to get aircraft safely through the NAS. You make the observation of professional pilots, and as such most of us have flown thousands of approaches. We know what the controller is going to say and we know what he needs to hear.