I've always gotten the impression that basketball has a larger population of fans who consider themselves "fans of basketball" rather than fans of a specific team. They flock to whatever team they think happens to be most interesting at the time. I have a friend from Minnesota who has, in the few years I've known him, gone from being a Magic fan to a Thunder fan, because he likes teams with a solid young core and switches his allegiance to a new one every few years.
Combine this with bandwagoners that plague every sport, and you have a lot of Laker fans on the East Coast, Heat fans in every city, etc.
