Whisenhunt has been there and done it before, so he was probably looking for certain things with his second head coaching gig.
We'll never really know if he chose Tennessee over Matt Stafford unless he comes out and says it.
If it were me and I had a choice of gigs, I would go where the QB situation is best, or the one where I am allowed to make my own decision with the QB spot, that way if I am getting fired, its because I fucked up, not because I got stuck with some other guys QB who failed.