Regionalism, travel, market....All things that we should account for.

1) the PAC is done...politics will not allow expansion into areas where the political views are not in line.

2)B1G-they need something substantial. Big Ten football has been described as being as exciting as watching paint dry. Even Ohio State/Michigan is a boring game with just a lot of hoopla.
What they need is Nebraska v. Oklahoma, a western anchor rivalry to offer some hope for B1G fans to see something exciting. Throw in Kansas to the B1G too, they are a great afterthought.

3) SEC.....what do you give someone for Christmas when they already have everything? Why something big and flashy, just to make them feel important and then some small trinket because the color is nice. Bring on the oranges: Tejas and Oklahoma State and the political tag along (Texas Tech).
Texas Tech helps make Oklahoma State relevant which in turn helps make Missouri relevant. Oklahoma State also gives the SEC quite a bit of leverage over the B1G/Oklahoma.
But wait that's too many because we all know two things are sure in realignment 1) nobody will go beyond 16 teams and 2) Notre Dame is not going to join a conference unless they have to. The solution of course (as it always has been), is to slide South Carolina back into the ACC.

4)ACC-South Carolina keeps the ACC in a slight numerical advantage over the Big east and completes the the ACC/Big East merger. West Virginia takes the 16th spot to, as someone aptly expressed; "ties the room together".

This scenario give everybody something, but most of all it gives ESPN a dominating position product wise and the positioning of Missouri disrupts the B1G's flow and limits their influence due to a lack of population.