I'd imagine most unhoused individuals are doing it as a strategic cost saving. Only, they're strategy involves eating and surviving rather than paying for unreachable/unsustainable rents. Maybe they didn't choose it, but it's still the strategy they're engaging in.
There are plenty of folks who can’t find housing for other reasons like background checks, credit score checks, etc. that might not be directly related to their ability to pay rent at that point in time.