Stallion and mustang1108 are right, for years there was a dearth of Texas QBs in on both college and NFL rosters because of the option oriented offenses of the 1970s and 80s. The 7-on-7 competition has really helped hone QB skills in the state.
But don't forget, the passing game was really developed in Texas at SMU and TCU during the 1920s and 30s. Ray Morrison's Flying Circus and Dutch Meyer's spread formation were decades ahead of their time. Even though he was a Frog, Sammy Baugh was the game's first modern passer and the greatest player in football history (Please don't say Jim Brown was, he wasn't and he didn't change the game like Baugh did).