The reason has evolved over the years. In the mid nineties, when I started watching the NBA, I really latched on to the Bulls and also the Charlotte Hornets.
But when the Celtics drafted Paul Pierce, that was it. As a young kid I finally had a reason to root for the hometown team. I am a die hard sports fan, but grew up in a household that rarely watched sports strangely enough. I remember watching the 96 Super Bowl by myself actually. My parents werent even interested in the local team in the Super Bowl!!!
This is why I had to find my own way when it came to which team to root for. I ended up landing on all of the local teams, but if it werent for Paul Pierce, I might be rooting for the Chicago Bulls, or the Pelicans!
After 99, I really started to dive into the history of the team and discovered a million different reasons to be a fan. But experiening Pierce's career as a Celtic from start to finish was pretty freakin cool.