Shocks me that USC can't hire a quality coach (they got Carroll almost by accident). Even more shocking that they haven't pulled off a splash hire in... ever.
They did get Carroll by accident. He was way down the list and just happened to be at a point in his career that he was looking for a way to revitalize it. I suspect sanctions are playing a role now. They're not out of the woods yet, and the effects will be felt for at least a season or two after they're fully lifted.
Sark knew his days were numbered at UW, and from USC's perspective he is disposable. The other candidates all had options, or didn't appear to fit (I'm thinking of Orgeron). JDR is an NFL coach and may end up coaching Houston, while Peterson got what he wanted all along (who knew he had been eyeing UW for the past five years?).
My guess is that they will make a splash hire three years from now. Hopefully by that time, UW has ascended to where Peterson sees the program belonging and it won't matter much who rules the PAC12 South.