That's not accurate. How is it that a hockey team in FLORIDA in Tampa is top 5-6 in NHL attendance... Hockey... in Florida. The TV ratings for the Rays are pretty good and the minor league teams in Florida get good attendance.
The issue with both Teams in Florida, but more so Tampa, is location, location, location.
There is one narrow bottle necked way to get to St Pete from the Greater Tampa/Orlando area. It sucks as far as traffic goes, getting there for game after work, parking and leaving after the game. There is no public transport. no Metro rail, no subway or commuter trains or busses.
The Marlins are more complicated, but basically at the crux of the issue is the same reason that Montreal lost it's Team in the first place. Same guy responsible as well...Fans of the Marlins are scorned and there are other issues, but years of selling off their stars and being a middling team has not helped.