Cities like Milwaukee have very low homelessness. Is it because the people there are just less mentally ill? Less prone to drug addiction? Of course not. (In fact in a state with cold, dark winters and where there is a bar on every corner, you’d expect the opposite.)

No, it’s because of the low cost of housing and because of their Housing First initiative.

Housing First works and it’s only because of a lack of political will that it’s not being used in more places.

Its also possible that it is very hard to be truly homeless in the winter in many places in the USA, and being someplace warm year-round, makes being homeless easier. Just like being someplace that is less likely to arrest you for openly doing drugs in public. If you make it easy to do drugs without consequences, easy to live on the streets year round, you are pretty much guaranteed of getting more of those things.

I live someplace where it routinely gets well below 0F in the winter, for weeks on end - if you live someplace like that, you do your best to make different life choices if you do not have a death wish.

You're neglecting to address enforcement issues such as Criminal Vagrancy which is strictly enforced in some locales and lax in others.