He's not been consistent with the way he's treated players.
Guendouzi's behaviour with Maupay was lamentable, but he's a young kid and he exiled him for reasons that still aren't quite clear. Yet Xhaka, who is a regular underperformer and does petulant stuff all the time, is selected, despite being a significantly more experienced player.
Then there's Willian. Not only did Willian go to Dubai during the international break, to eat at Saltbae's restaurant, he was clearly breaching lockdown rules at the time. There were apparently internal conversations about this, but he was selected for the subsequent games. Purportedly, this rubbed some of our other players up the wrong way because Willian is another highly experienced figure, was utterly careless during a global pandemic, yet wasn't punished at all. Not only that, but he has been absolute turd since his debut vs. Fulham and Arteta persists with him. Yet players like Smith-Rowe or Nelson barely get any minutes, when they've impressed in the Europa.
The William Saliba situation, a 19-year old CB we spent £27m on, has also been handled with such a lack of care, it's no wonder the boy is frustrated.
I refer you this:
https://www.football.london/arsenal-fc/truth-behind-william-salibas-exile-19513579
On top of that, he preaches about having the highest-standards and not tolerating players being idle. Yet Holding, Xhaka, Bellerin, Lacazette and Willian are selected EVERY week for not performing, and our youth, who have impressed in their cameos/minutes in the cup competitions, are lucky to have a spot on the bench for the league games. He's even selecting the likes of Kolasinac and Mustafi ahead of them, when they won't be here in the Summer!
He's also mistreated popular figures in the dressing room like Ozil and Sokratis, whom many feel have been hard done by. Now, they may not have a future at the club in the long run. However, you can't upset the morale of the dressing room by outright excluding them and limiting their influence instantly.
He says Ozil is being left out the squad for 'footballing reasons', when we're 20th in the league for chance creation. It makes him look absolutely foolish.
There's already lots of reports about divisions in the camp and, if that's the case, it's only a matter of time before the inevitable.