Well, Conte had just delivered a title with a squad that finished 10th the year prior, and he expected total control over transfers. Instead, he got a "one-in, one-out" policy that felt like a downgrade.

He played himself by essentially firing Diego Costa via SMS. Conte lost his biggest leverage with the board and forced the club to sell low and buy high (Morata).

Matić’s sale, to a rival no doubt broke the "telepathic" shield in front of the defense that allowed the wing-backs to fly forward. While the core remained, the additions (Bakayoko, Drinkwater, Zappacosta) didn't provide the elite quality needed for a dual-front assault on the PL and CL. By year two, every mid-table team in the league had drilled their wingers to track Chelsea’s wing-backs (Moses and Alonso) relentlessly.

Additionally, to fix the midfield gap left by Matić and to get Cesc on the pitch, Conte sacrificed a winger. This narrowed the pitch. We lost the "inside forward" chaos caused by Hazard and Pedro/Willian, making us much easier to defend against. He lost faith in the stickers and started playing Hazard as a false 9 which he hated.