Why do some cities have two teams in the same sport while many other cities have no professional team?

Cities with Two Teams, Cities with None

It all comes down to money. Some large urban centres (New York, Los Angeles and Chicago) have such a large populations that they can sustain two sports teams, like the Yankees and Mets, or the White Sox and Cubs. Other smaller cities, for example Memphis, have such a low population in comparison the the others that they can not even sustain 1 professional sports team. Take baseball for example, the yearly salaries for the average baseball team is about 70-80 million per year. The average stadium holds 38-60 thousand people per game, for Memphis that's about 10% of the population. Chances are that a baseball team in Memphis would not sell enought tickets or merchandise to break even. Given this there is no reason for investors to put money down in smaller cities.