That's why it makes sense to go to a school like App State to get a DC (or OC if CPJ wasn't our OC). An established DC on the P5 level isn't jumping ship unless he's either on the hot seat at his current school, in which he's not doing well so they're looking to replace him (see: Ted Roof), or another school is offering him such a large increase in his salary he almost has to say "yes".
Hate to say it, but right now GT is a lateral move at best for most P5 DCs. No one is leaving a job they know and doing well at for the same job with far less certainty. GT just missed a bowl, our HC is older, and he's going on his 4th DC in 10 years. That's not a good situation for an established coordinator at the P5 level to leave a job for, especially if GT can't offer that guy a substantial raise than what he's already making. GT can't offer that.
Someone outside the non P5 level would absolutely bite at a school like GT. It gives that candidate the opportunity to move up and coach at the highest levels, more resources to coach, and will probably more than double his current salary. $600-700K is a BIG raise for someone making $250K. For someone already making $750K+ (which is what a good, established P5 DC is making) a raise to $800-900K isn't as substantial to take the risk on a situation like GT.