Why do many people call new Miami Heat fans bandwagon fans?

Let's face it, the Heat had far less fans before than they do right now. But ever since they got a bunch of all-stars, a lot of people switched teams. I also used to like the Spurs and Boston before. But now the Heat have a better team, so I couldn't care less about the those teams. It's just smart to root for the team that will win many championships and many people are like that. Do you know how many people I saw running around with D Wade and LeBron jerseys? I didn't see them 1 year ago or more.