The human mind is a funny thing.
You're assuming that the individual isn't affected by social factors, and that he can effectively isolate himself from negative demands and expectations. But if research in social psychology has shown nothing else, it's that the individual is not separate from his social environment. Even when we know better, when we should be able to rationally extricate ourselves from a situation, we continue on in it for a myriad of reasons.
We see the warning signs, only to blindly rationalize them away so successfully that they disappear from conscious thought. I've been there, and I've suffered the consequences.
Take an external authority figure, in this case a boss who values a person's ability to lose themselves in their work in order to get things done, and sit back. Add in a culture of co-workers who celebrate the same. Maybe the employee wants to work their way up the ladder, or maybe they just want to get the satisfaction of positive feedback from those figures. Watch as these factors slowly influence the employee's sense of perception, and eventually through it, their behaviors and how they judge them. Eventually, you'll see a affective and cognitive responses as they integrate these changed beliefs into their self-identity. This is made all the easier by the presence of authority figures
You see this everywhere. Why do young investment bankers accept the idea that they need to work upwards of 80+ hours/week, and often, 100 or more? Worse, they not only accept it but they make it part of their core self-identity to be celebrated. Why do undergrads pull all-nighters and consider them a badge of honor? Or far more darkly, why do so many battered spouses stay with their abusive partners, justifying the abuse as something they somehow "deserve?" If someone tells you that you're dirt enough times, eventually even the strongest-willed of us will start to question it, and far too often, come to believe it.
Across all these examples and more, the same cognitive phenomena are at work. You think this is solely a matter of willpower. It's often not. Yes, he's pushing himself. But social factors are also pushing inward on him, making it easier to do so.
I'm not belaboring your end point. It's a good one, and the presence of outsiders willing to give such advice--get out, get somewhere where you can rebuild your sense of self and personal boundaries--can help empower people to act on it. But don't assume that it's as simple as turning off the screen, or that you're immune to these pressures. You're not. No one is.
Given enough time, even the strongest can and will be influenced by social factors. Often, to positive ends. But not always. Given enough of the bad, eventually, everyone breaks. Not at once. Never at once. But little by little, piece by piece, people will change without even realizing it. And once you're there, the mind's ability to rationalize and protect itself will help keep you there.