Not only that, but given that the end of the race is 7 laps of the Champs-Élysées, the riders will be able to see any break-away riders ahead of them, which always gives the chasing pack a bit more of an incentive.
I think there might have been a case a few years back when someone broke early (half a lap to go?) and stole the stage from the sprinters, but I don't recall a case in recent times when the top end of the race order has been changed, other than the mentioned Lemond/Fignon TT. It's just not the done thing.