The parents certainly can be enabling, but I think you're ignoring that there are plenty of people that are homeless, that do wind up with dependencies on alcohol, drugs like meth, etc, and your implication that anyone (especially people in their 30s with no real work history) can get full-time, minimum wage work doesn't seem realistic. Many of those jobs are both minimum wage and few enough hours per week (to avoid having to give you benefits, of course) that it would be extremely difficult to live independently, while still requiring a schedule that makes it nearly impossible to take on other jobs.

I'm in my 30s and have now seen several high school classmates with similarly poor prospects eventually succumb to drug overdoses.