This is a really good point. I have raised teenagers, we can try to encourage them to do things, we can give them options, we can make them appointments or whatever, but we can't make them do anything. So who knows, maybe someone did try. JMO
Perhaps kicking them out of their respective homes was the attempt to make them do something (and they did - they left). You definitely can get teens out of your house, if you want to.
Also, you can control their spending in so many ways. Phones and Steam games cost money. New games cost money. No parent has to pay for those things. And no custodial person (grandmothers included) have to permit those things to be used in the house. Impossible for them to play those games at the library, btw (computers aren't good enough).
So there's a lot that parents can do, if willing, to reshape behavior. Of course, if you're already scared of the kid(s), that's a bit different.
Lots of my students are under a "you go to school and getting passing grades or you're out of here" policy from their parents. Many of them go homeless, temporarily or permanently, due to this. They learn to cope (and in many cases, decide to stay in school and end up taking that minimum wage job they refused the year before).
Oddly, so many students who are more or less on their own...do very very well in school, even with a past track record that's poor, once the limits are set and once they realize what it's really like out there.
There are also students who must attend their psychiatric sessions and take their meds, or they are going to be out of the parental home. It often takes a brush with the law, though, for them to really get this.
It's hard, because the years from about 17-25 are the peak years for onset of schizophrenia, schizoaffective, major depressive disorder, and bipolar. It's hard for family members to see it, sometimes. Schizotypal disorder can be and is masked by video games (and in some inpatient units where I've worked, video games are used as today's panacea for schizophrenics - television used to do the trick).