Homelessness has generally been an addiction / mental illness problem, but in HCOL areas it's probably also something that sweeps up non-neurotypical people who are not able or willing to prioritize a high-earning career.
In HCOL areas, dedicating oneself to art, music, volunteerism, care of a disabled relative, or anything other than corporate work can result in homelessness. Even if one gets a low-paying secretary/warehouse/retail job, one can end up pitched onto the street if roommates fail to pay or a minor medical issue needs treatment.
There is a certain coerciveness to such economies. No evil villain is saying "we have ways of making you work" in a threatening tone but when expenses are high, one's own wages are low, and there is a hard floor on rents, running out of money can happen fast and as a result of relatively minor setbacks such as car breakdowns, accidents, etc. The system itself punishes anyone who refuses to, or can't conform.