Politics. Everyone I know who moved from NYC to Florida did so because they were sick of the politics, and wanted to live in a red state with NYC-ish amenities. Miami is absolutely that.
For most though, it's about housing cost - those move to Jersey or MAYBE LI. That's a larger group, too.
Your forgot one of the biggest reasons:
Florida has no income tax.
And there isn't a lot of politics in Florida...just leaning in the opposite direction?
yes, these are Republicans leaving
The amount of money you can save moving from NYC to Miami starts to become pretty substantial if you make over 400K, and Miami has basically all of amenities of NYC with less bullshit. Miami is far from perfect obviously, traffic is horrible, the NYC food scene is much better, and there are probably a lot more people with guns.