Thought the exact same thing after last night's game. In the write-up by Ian Browne, Hill blamed himself completely for the 5th because he flat told Cora he was fine when he wasn't.
Cora said Robles was excellent in his first 8 games, but now his breaking stuff is too flat even though his velocity is still good. He also said that guys--meaning relievers--must contribute. Robles is the 4th highest paid reliever on the Sox @ $2.5M.
If you read me on the game thread I named a bunch of culprits for the loss: Hill for staying in, Danish for walking in the 3d run, Robles for being awful and getting charged with 3 runs, Diekman for the wild pitch which brought the 6th and winning run for the Cubs, and the lineup for scoring 1 run in the final 7 innings. I also pointed out that the 3 runs in the 2d for the Sox depended on a walk and an HBP by the Cubs starter. I left out that the Sox pitchers had 10 BB's in the game, including 4 by Hill and 3 by Robles.
So of course I blame the players far more than Cora's decisions. That said, at the end of the season (or earlier), managers are graded on wins vs. expectations.