That's because teams are owned by private business (mostly). When they can't draw enough fans in one city, they move the team to another in an attempt to draw the fans there. The most notorious of the moves involved the NFL (US Football) Baltimore Colts who packed up and moved in the middle of the night to Indianapolis.

An interesting note about team ownership, and why I said "mostly". The Green Bay Packers of the NFL are owned by the city of Green Bay.

>Yeah, curious this business of moving the team to another city. It's like moving Manchester United FC or Totenham Hotspur (Spurs) FC to another city but only taking the suffix part of the name.