When it snows, life becomes impossible without a few thousand dollars worth of equipment, so all the mentally ill humans go south where surviving means wandering around and scavenging for food. Travelling a long distance is also a big ask, and so those people don't go north again.
And so Florida bottlenecks and then keeps all of these people.

Also the cocaine trade built Miami, all the boomers are moving there because they hate the snow, and in the middle of florida is a giant indian reservation filled with the indians who decided to stick it out on the reservation instead of assimilate, so they perform menial labor jobs like it's a low 2nd world country.

Couldn't get out of there fast enough. The state has serious issues. Also heat makes mammals angry and holy moly it gets hot down there.

The whites can live because they can hop between air conditioned house, air conditioned car, and air-conditioned workplace and air-conditioned recreational areas.