The reason Kansas State and Iowa State are in the Big 12 (or Northwestern is in the Big Ten, or Mississippi State is in the SEC, etc.) is not really relevant to expansion today. But geography created interest years ago that persists today. It's why a dormant rivalry like Kansas-Missouri is more important than UCF-USF.

Schools already in the Big 12 have decades of being in the public eye and that gives them a considerable advantage over UCF from a marketing standpoint. K State and Iowa State aren't Texas, but people know that Bill Snyder has coached Kansas State for decades and had a lot of success. People know that Iowa State is consistently competitive, that they win in basketball and are always prone to pull the upset in football. Those schools fill 50,000 plus seats in their own stadiums and travel well. Neutral fans recognize those brands and are more likely to watch Oklahoma-Iowa State than Texas-UCF (unless UCF is 12-0 and playing in a major bowl).

If history began today, UCF might be more prominent and marketable than Alabama.. But history didn't begin today. Schools like UCF and UConn and Boise State are thought of differently than schools like K State that have been competing on a national level in power leagues for decades. Tech is the poster child for being given an opportunity and taking advantage of it. But those opportunities aren't going to be offered much anytime soon.