I don’t know why Moises Caicedo was benched but a player like Caicedo should not be left on the bench if he is not injured because we can all see the difference in their midfield compared to other matches he started.
I can’t say for sure but I can still recall hearing over the commentary that, he happens to be the last returning player from the international break on the Chelsea team. That could mean, not having to be properly filled in on the team tactics and perhaps, leaving him on the bench was by some means to discipline the player.
On top of that and recent performance for Caicedo I wouldn’t say he was just too great or his coming off the bench could have been part of what resulted to this defeat. I can still recall his first game where his mistake caused Chelsea a goal, a few games after that where he struggled and even games where he had to be on the starting lineup and Chelsea still gets to struggle.
Chelsea is a team that lacks consistency on their side and while they still try to fine a rhythm for there team, you can expect whichever opposition to capitalize on that, cause them to make a mistake and use that to punish the team. There were just lots of mistakes from them today and each of them was punished.
In this instance, the lack of consistency is likely caused by the younger team, which management does not seem to understand. Newcastle is slightly different from Manchester City with the experience in the squad. The team started a new central back and new defensive midfielder that should come later in the Game.