That could be a reason and I'm not saying it's not the case, it's the repetition that is tiresome, like every 2 post in a same thread speaks of Marrone's stubbornness.
Let's explore another possible scenario with Urbik (totally applicable to Mike Williams case):
Lets go back to training camp, where all jobs are up for grabs, Urbik is not the greatest guy on practice, he is probably better than Pears and Richardson, but he doesn't have the fire or shows the fire to earn the spot on the starting team. Meanwhile the coach moves some of the parts and gives the job to those that earn it on the practice field.
Marrone sets Urbik asides and tells him that he's the better player but that before he gives the job to him he needs to see better effort, otherwise the guys busting their balls for it would not care if the guy horsing around or not caring gets the job, why have practice in the first place?
Urbik sees his teammates failing and tells to himself that he has been selfish and realizes that he has to go back and his attitude towards his role on the team changes.
Marrone wants his players to earn playing time.
I will copy and paste this one, every time people calls Marrone stubborn about not playing Urbik.