The Big East wanted to add the Boise St. Broncos to join in 2012 instead of 2013 to likely to replace the West Virginia Mountaineers who seem to be off to the Big 12. However, Boise State president Bog Kustra came out and said that there is no way that Boise State could make the move to the Big East a year early (via Big East Coast Bias):
"It's too late. I can't imagine how anyone can pull that off. We would never want to pull it off in a fashion that dealt shabbily with our existing partners in the Mountain West. I don't think that could ever work," Kustra said.
Not really sure it is too late to make because the conference schedule for football would be seven games for Boise State and they would only need to schedule one more non-conference game, but the real issue could be with their other sports to the WAC.
Or, it could be that Boise State does not have the money to pay the exit fee to leave the Mountain West and that is what Kustra is meaning by it being too late. The amount of money that Boise State would have to pay would be somewhere between $7 and $9 million, and the amount of the Big East television deal is likely not enough to offset the extra cost for leaving the Mountain West early.