I'm sure plenty of streamers have such an awful schedule because of their mental health--not for their stream. I doubt they underestimate it, but it's hard to fix when you're not doing great. Messed up sleep schedules is a common sign of depression after all. And like you said, many of them don't go out, and rarely socialize irl (you need human contact). They often live incredibly unhealthy lives, both physically and mentally.

I've seen so many streamers mindlessly keep playing their game until sun up, acknowledging themselves they should have gone to bed earlier. I hope it can get better over time, but perhaps it shouldn't be surprising that a profession/hobby many get into because they either need an escape from real life, or are addicted to games, isn't that great for mental health.