I do think it may be a case of no incentive but also being a case of being in denial or dissociation where the issues are not really even truly being processed - (in any kind of positive constructive way). Of course I don't really know if I'm only considering my own experience or if it could apply to what you are talking about here as well.
Like, just one example: Say you have trouble sleeping. Now imagine you share a bed with someone else who has trouble sleeping. Now the both of you are keeping each other up because now you have someone to talk to when you can't sleep. Now add in a roommate who keeps weird hours, so you have someone to keep you company even when your sleepin' partner is actually sleeping, so you have even less incentive to try to keep to a regular schedule because none of you have stable employment and no real structure to your lives, and now all three of you are napping two hours here, an hour there, having an occasional 12-16 hour marathon sleep session, all just at whatever times, until the very idea of regular sleep and wake cycles feels unnatural and forced.
Apply the same logic to drug use, or to self-harm, or to compulsive rituals, or to bringing home more fucking stray cats (I'm positive that all of us had toxoplasmosis, fucking thanks Dawn), and even though on a certain level you're aware that most people don't live like this, it all starts to feel normal.