Bubble screen oriented offenses and passive defenses. Bubble screens thrive only when defenses don't bother to blow them up. This year only one Big 12 team -- Texas -- allowed fewer than 6.5 yards per pass attempt. The SEC had 8. In 2008 no Big 12 pass defense was below 6.6. The Big 12 has comfortably settled into a mindset that short passes will be tolerated and allowed to ramble. Consequently the quarterbacks have automatic cheap yards available and the little details aren't a concern.
Fans love to rip the Pac 12 but it's been a pro style league for decades, so not surprising it has produced so many top quarterbacks. It will be interesting to see what happens now that some gimmick coaches have filtered into the league at Washington State, Arizona State and Arizona. I suspect Mora Jr. will run a more traditional Pac 12 offense at UCLA. Heck, Kiffin ran plenty of bubble screens at USC last year, taking advantage of the terrific young receivers. Carroll never threw underneath to that extent.
This dude here has forgotten more football than 90% of the posters here combined currently know.