In FL you pay sales tax on everything. It’s the reason you see so many trailers tagged in OK and Maine. A PA carrier even tagged their trailers in Maine, even though PA was exempt from sales tax, to make the trailers exempt from PA inspection requirements. They had about 4 trailers per power unit at the time.
The reason they tag them there is because they get permanent tags. I tagged all my trailers in Alaska way before I moved here, just because I The local DMV in New Mexico was a hassle because I had just a bit too light of skin color.