The difference between what clients and drivers see goes back to this: drivers are heavily scrutinized based on their ratings, and it is important for them to associate the rating they were giving to the trip that actually occured.
Drivers know this and are instructed not to do it (same goes for soliciting a 5-star rating at the end of a trip, for that matter), because it so greatly undermines the confidence our customers put in Uber in the first place.