Most of it has come out already. He wants to be a head coach badly, and he needs to boost his resume. CSU straight out told him he needed to add more titles to his resume if he wanted to be a serious candidate. Going to work for Urban, where he can now add "associate head coach" (or whatever it is) is a step up for him. People that don't know football and how it works will tell you it's a title in name only, but he'll have a lot more duties on the administration side of things that head coaches do, so the experience will be invaluable.
A reporter friend of mine who knows Alford well told me in late December that Alford wanted out of South Bend because he needed to add to his resume. So this is not a shock to people at ND (a shock to fans, for sure). What was holding him back was that he was making a competitive salary here (while asst pay is lagging, he was doing just fine), and his deceased brother's family is living with him now. SO he couldn't take a pay cut to go to a smaller school. But OSU offered him a good salary, and like I said, a chance to enhance his resume. That was what sealed the deal.