5) Kentucky Cornels
Prior to the ABA-NBA merger in 1976, the Kentucky Cornels were the most successful team in the ABA. They won the most games in ABA history, including a championship in 1975 and had Hall of Famers like Artis Gilmore and Dan Issel.
The Cornels weren't absorbed by the NBA, however. Actually, their owner accepted a buyout, which he used to acquire the team that would become the LA Clippers. Since then, Kentucky has proven to be a great basketball state and has supported the Kentucky Wildcats, suggesting that they could support a professional basketball team once again.
Admittedly, a population of 4.5 million is on the small side for a state to have a professional team, and the NFL and MLB don't have teams in-state. Then again, the state's population has steadily risen, going from 3.4 million during its ABA heyday to 4.5 million now.
That is larger than Utah, Oregon, and Oklahoma City, but each franchise has thrived in their respective states, partly because there are no other major sports teams there. The league could have similar success in Kentucky, too.