Do you know the largest market in the US without a major-league team in any of the four major sports?
My guess would be Austin, Texas. Longhorns have enough clout to keep pro teams away. City population of 930,000 and metro population of 2 million.
Maybe a little bit of a thread slide, but I've noticed most places are either college towns or pro towns. Nice thing about being a college fan is your team probably isn't going to get up and move.
Portland Oregon has that honor now, I think.
Perhaps Mobile or Birmingham Alabama.