I think in addition to the lack of performance these past couple of years, Lewis is also really frustrated that he seemingly hasn't built up enough trust and goodwill within the team (at least amongst the engineers) that his suggestions aren't listened to. Commentators always praise the likes of Schumacher, Alonso, Vettel and now Verstappen for their driving I.Q., but always try to play LH for the dunce. And now it seems like his own team may have taken that view and it's not sitting right with him (as it should not).