Big12 only has one major recruiting ground (Texas) and very few markets. The struggles make sense. In fact, the Big12 should be worse than it is currently (by currently, I mean last 4-5 years. I know they are bad this year). Teams like Oklahoma State and Kansas State keep you guys relevant when these programs really shouldn't be that good. No way Oklahoma State should have a better program than Georgia Tech or Pittsburgh for example based off the resources at the disposal of those ACC schools as opposed to Oklahoma State.
Pac12 only has one major recruiting ground as well, California, and suffers from a populace that is disinterested and being in a different time zone that is 3 hours different from most media markets.