Should also point out that Miami in general is not a sports town at all. Outside of the Dolphins (who have been mediocre at best since Marino retired), all their pro teams are 30 years old or younger. They are just now beginning to experience a new generation of fans. The Heat had the biggest bandwagon fan base in all of pro sports for about 4 years and now no one pays attention to them outside their own fans, the Marlins and Panthers have passionate fans but also have attendance issues, even U of Miami football was struggling until Richt came in.
Don't get me wrong, I'm not criticizing the Big 4 for having a prescene there. They should, there's something like 6 million customers to attract. If I were a professional athlete I'd love to play there. But there's so much more to do in South Florida than watch mostly lousy uninteresting teams, which is what the Heat/Marlins/Panthers/Dolphins have been minus a few years of LeBron.