Its a pride issue. He has accomplished what he has wanted to accomplish at bama. Same as he felt in Baton Rouge.
Why did Nepolean feel the need to conquer the known world?
Maybe...but at the same time, Saban has already conquered the college football world. I hate the guy and I think people worship him way too much, but he is a damn good coach. I don't think moving to Texas is going to prove anything that he hasn't already proven.
If he really wanted to prove himself, he'd go to an upcoming but still shitty school, make it a national contender within a decade, and then be like, "What, bitches? G.O.A.T.!" Making Texas a national contender is not a challenge, and wouldn't be any different than what he did with LSU and Alabama.
That's why I think he tried his hand at the pros. He wanted to show that he could do something that he hadn't done before. But he didn't do so well at that, so he came back to college football. If Saban isn't going to attempt to resurrect a dead college program, then I don't think he's going to be making a more or less lateral move to Texas or any other similar football school. At least not from the point of view of trying to boost his pride by proving something, because he's already proven it at the collegiate level with powerhouse schools.
Of course, money and awesome benefits could change that, but like THS said, I think Bama would match any offer without batting an eye.