Probably because Florida is the most tropical area in the U.S. Warm-weather critters can make a go if it there.
The flora and fauna of North America is still recovering from the last ice age and that is the reason invasive species do so well there. There are so many ecological niches that are still left open that new feral species fill them rapidly. Native North American fauna has not had time to adapt fully to Florida and are often out competed by invasive species.