IMHO,
It all goes back to Texas. UT made a deal with ESPN for this Longhorn Network. The lesser schools in the Big 12 accepted that, having no leverage. At the end of the day, it gives Texas a revenue advantage that no other conference would tolerate. The better schools then left (Nebraska to the Big 10, Colorado to the now Pac 12, and Missouri and Texas A&M to the SEC).
Meanwhile, the Big East was dying. Its AQ status in the BcS has always been undeserved, and was becoming undefendable. And in basketball, 18 is simply too many. So Pitt and Syracuse moved up to the ACC.
Utah takes the oportunity to move up to be the 12th member of the now Pac 12, and BYU becomes an independent, similar to its fellow religious school, Notre Dame.
At this point, note the TV implications. The SEC picks up St. Louis, Kansas City, and Texas A&M is followed statewide in Texas, the fastest growing state. Salt Lake City is the fastest growing metro area in the country, and the LDS church is the fastest growing religion in the world.
So WVU is despirate. It is, exempting its 3 easternmost counties which are bedroom communities for DC, filled with people from other places and uninterested in the rest of the state, losing population in every census since 1930. It is willing to accept being unequally yolked with Texas and joins the geographically illoical Big 12.
So the last shoe to drop is the death throws of Big East football. It wants to, again, raid CUSA and try to sell that as major football. Probably won't work.