This is single biggest reason that the SEC is so good. It covers the areas where the most players are. It's also why the B1G has to innovate so much to overcome that.Also, outside looking in, the SEC is currently in a smaller footprint, but within that footprint, you have some really solid recruiting states. One thing I think that will be an issue for the two 'Big' nationwide conferences is going to be recruiting. You're already seeing a lot of the existing Pac student-athletes voicing their opinions about not getting to play in front of their families.
For example, let's say Florida State and Miami were to join the Big Ten. As a recruit in Georgia with offers from UF, FSU, and Miami, would you go to Florida State/Miami knowing there's a chance that by the time you're actually playing, their conference away schedule could include Washington, California, Minnesota, New Jersey, and Michigan or would you choose Florida where your conference away schedule could include Georgia, South Carolina, Mississippi, Louisiana, and Tennessee. I get there are players that want to distance themselves from their homes, but I think there are a lot of players that want their families to be able to see them play.
It also makes Clemson and Florida State much more important. It's real simple to me. Get those two and 2 of UNC/NC State/Virginia/Va Tech. Then you are set as a conference.