Nah it's not that, it's basic big fish in small pond coupled with victim mentality. The star becomes bigger then the club and can't do no wrong in their eyes. Similar thing happened alot with Totti in Roma.
Sarri defended him and has been kissing his ass (saying whether he starts vs Villareal was up to Higuain was worse) because he wants to increase the odds of Higuain remaining at Napoli next season.