Acting like an idiot? Martial plays for a top club and is competing with one of the World's best players and a great talent in his position. It's very similar to his issues with France.
If I remember rightly, Martial, like with United started off his International career very well, but a very "Martial-esque" off game for France saw him out in the wilderness and now Deschamps struggles to fully trust him. It's a similar story here.
That said, I think Martial is a great talent and absolutely wouldn't want him to leave, but to make out "it's all nasty Mourinho's fault" is plain bollocks.
He didn't start very well, he showed promises but was never in a position to seriously start. Out of all the players mentioned only Lemar started very well and almost immediately competed for a starting position, Mbappé improved after every games, like Dembélé. And Martial didn't lose his place because of one game, first he didn't had a place and secondly the chance was tactical, the team needed a playmaker like Payet in order to allow Griezmann to play closer to Giroud.