Part of the problem in Florida is how oversaturated it is with sports. 3 NFL teams, 2 MLB teams, 2 NBA teams and two NHL teams. 9 teams is a lot.
On top of that, those pro sports also have to compete with college sports, especially college football which is probably the most popular sport in the state. So you can add in another 3 major teams (FSU, FU and Miami) to go along with another good team (UCF) and 3 other D1 teams (USF, FAU, FIU). Sports fans are getting spread pretty thin at this point.
Then there are a lot of transplants as people mentioned, combined with a lot of those teams being pretty new and also not having a ton of success. Just not a great way to build up a generational fandom.