Here is a link to the United States DMA map -
http://seventhpoint.com/images/pdfs/2012...%20Map.pdf
When looking at what adds value to a conference you either have to add a nationally followed program, or one in a high population area, or one in new territory. This is the paradigm of expansion in going from 12 to 14. The Big 10 added one average and one really bad program but obtained entry to the NYC DMA, the DC and Baltimore DMA's. DMA's can and are shared. It's impossible for a single school to provide enough programing to fill the sports channels with 30-50 hours of live programing a week.
As far as the ACC goes, Va, VT, and Pitt penetrate their local markets and those markets spill over into the Tri-Cities TN/VA, Bluefield WVa, Salisbury MD, DC, and Youngstown Ohio. This doesn't mean that Pitt is the most popular team in Youngstown, or that UVa is the most popular team in the Tri-Cities.
The reason I mention Iowa State, is clear when you look at the DMA maps. There are just two programs in Iowa - Iowa and Iowa State. ISU is not the most popular, and it's probably third at best in the Western Part of the State, but in order to sell ads to people in Iowa, the tv and radio folks in the Quad Cities, Sioux City SD, Omaha Neb, and Rochester Minn, have to cater to the ISU crowd at some point during the week.
You can see this by looking at the DC DMA, half of it is Northern Va, just like half the NYC DMA is in NJ.
The ACC will not add, nor will ESPN pay for an expansion that does not expand the particular conferences' network potential unless that program is of national significance.
Now, let's go back and look at everyone's 13th and 14th program -
SEC - TAMU and Mizzou - are these football powerhouses with large national followings? No. But they put the SEC in Texas, Kansas City, and St. Louis.
ACC - Pitt and Syracuse - are these football powerhouses with large national following? No. But they put the ACC in NY State, NYC, Pittsburg, and Western PA.
B10 - MD and Rutgers - we know these are not football powers but they put the B10 in DC, Baltimore, and NYC (The B10 had a foot in southern NJ via Philadelphia and Penn State).
ACC - Louisville - when the ACC had to replace MD, they went into virgin territory for the ACC and took the largest DMA footprints they could get - the entire State of Kentucky, and Southside Indiana. Look at the Cincy DMA in particular, it caters to Cincy, SW Ohio, Northern KY, and SE Indiana. Making Cincy somewhat, but not completely redundant for the ACC.
While it's true the ACC does not have a network at this time. They will, but even if they did not, that would not change the fundamentals of expansion since it's about making more money.
If you are ESPN, where does WVa make you the most money? In the SEC of course as it puts the SEC in the Pittsburgh, and DC DMA through WVa.
How do maximize the value of Iowa State? In the ACC
Every conference makes money with Texas, but not every conference would make more money with Iowa State, WVa, etc.
Cincy adds the most value to the B12. They are redundant to the B10, of very limited value to the SEC, and are of moderate value to the ACC. It's just a function of geography.
There are only a handful of programs that will turn on TV sets even when their programs stink. Notre Dame, USC, Texas, OU, Alabama, Florida, FSU, Ohio State, Penn State, Michigan, Miami, Navy - for other football programs, they have to have a good team. As far as expansion past 14 goes, unless one of the above schools is involved, new territory is what ESPN seems willing to pay for.