And there are untapped markets out there.
Such as? I'm not saying you're wrong, but I can't think of many US markets that seem like logical fits for baseball. Vegas of course wants any kind of major league team it can get, but basketball probably makes the most sense there (indoors, smallest arena, the city has a hoops tradition w/ UNLV, season lines up with their highest tourist time of year, etc).
It seems generally when leagues expand they do one team in the West & another in the East (i.e. Rays & D'backs, Raptors & Grizzlies, Rockies & Marlins, etc). I can't really think of an Eastern market that seems like an ideal fit for the MLB.....Charlotte maybe? But NC already seems spread thin between the Panthers, Bobcats, Hurricane & Tobacco Road schools.
Currently the largest MSA's in the US to not have MLB teams are:
13. Riverside-San Bernadino (4.2M); unlikely to get a team due to the proximity of LA, LAA and SD.
23. Portland, Oregon (2.2M)....do they seem to be a great fit? I dunno...meh
24. Sacramento (2.15M)...they can barely hang onto the Kings and have the Giants and A's not too far away.
25. San Antonio (2.14M)...its a fairly good size market with only one pro team (Spurs), so maybe.
30. Vegas (1.95M)...discussed above
31. San Jose (1.83M) too close to SF & Oak
32. Columbus (1.8M) doesn't seem logical, too close to Cleveland & Cincy
33. Charlotte (1.75M)...maybe, I dunno, doesn't seem like they're dying for baseball.
34. Indianapolis (1.75M)....maybe? Seems like for a mid market like them having NBA & NFL is probably enough, but they don't have anything in the summer.
Then you start getting into Cities like Providence, Oklahoma City, Salt Lake City, etc. Maybe SLC, they just have the NBA & MLS, maybe they'd be a fit but it seems like there just aren't many obvious markets that are obvious fits for the MLB.
6 divisions of 5 teams each works out pretty nice, I kinda think the MLB will be happy to leave it at that for a while.