It's perplexing - whatever's gone wrong with Fed. It's not just old age, loss of form or motivation. Sure there is some of that, but doesn't explain it all. Could be persistent injuries that Fed hasn't talked about and this could be why he's overhitting his ground strokes and making UFEs like pulling the inside in FH way wide.
Maybe it's because Fed was always a good front runner, but now that his form has come down, he's having real trouble and any and all of his weaknesses such as the topspin BH during rallies are coming into sharp focus. Opponents are no longer going into the match thinking they are going to lose.
Yeah, maybe a lot of it is confidence.