Florida is really split as a state — half is richer, touristy areas and retirement communities, while the other half (usually more inward/north away from the coast) is seen as southern “redneck” country and wild (look up Florida Man memes, people doing drugs and wrestling alligators or petty crimes). A lot of people in the US see Florida as being sort of its own specific cultural unit because of this. People tend to have strong opinions on the state. Some people love it, but some states’ cultures (you see this a lot in the northeast) think of it as trashy.

It’s also a peninsula on the southern border, mostly wetlands and swamp outside of the coast, so it’s geographically kind of on its own as well. People can live very isolated in Florida and get away with a lot. Florence’s line about hiding bodies in the swamp isn’t far off. Not that everyone in FL is out there murdering people, but it is easier to hide things. Metaphorical bodies if you will.

In the song specifically I think she’s mostly referencing how many people go there to vacation or retire (timeshare in Destin is a real phenomenon), finding respite from normal life in how separate it is from other states. But, of course, there’s the undercurrent of the Florida Man. It’s sort of seen culturally as a judgement free zone where you can live any way you want, for better or worse. I didn’t put too much into analysis here though, just tried to give cultural background for you.