My opinion is he's over reliant on players, rather than tactics and systems to create chances, so if the game changes are already out on the pitch he's reluctant to take them off, regardless of performance.
Rashford got hooked tonight because he was a passenger, but it's not an isolated performance from him in recent weeks. The difference this time around is that he has Pogba, another player that he trusts to create something out of nothing, ready to come on. If Pogba wasn't on the bench, Rashford would've seen out the 90.