Assume, for the sake of argument at least, that Stoops was contacted in late 2009 to gauge his interest in a job he eventually declined to pursue. Why come now? Because much has changed since then.
Most notably, the Big 12 began to fracture only months after Stoops decided to stay at OU. Not only were some of its most attractive programs poached, it's flagship school in Austin has suffered years of turmoil. A&M's defection means an SEC recruiting foothold in Texas, a state Oklahoma must draw heavily from.
The structure of how championships are determined has also shifted. Even with a title game, Big 12 teams seeking the playoffs will face charges of lackluster schedules. Notre Dame regularly plays USC, Stanford, and one of Clemson, Florida State or Miami. The Sooners' biannual trip to Morgantown has usually counted as one of their marquee matchups.
Bo Pelini, his former assistant and former Big 12 head coaching colleague, is back at Youngstown State, where Bob's brother is an assistant. Bo's son will be in South Bend, starting this fall.
He undoubtedly has great affection for and many friends in the OU program. He's not leaving them in any sort of lurch: they have the coach they want, and that man is obviously one Stoops trusts as well. His legacy is secure.
Notre Dame itself is a much more attractive program. Even despite Kelly's recruiting failings, there is more talent in the program now than when Weis left. There are several new facilities coming online (albeit some of them ugly). The University has upped its financial commitments to assistant coaches.
Bob Stoops' first road game as a head coach was at Notre Dame Stadium. His team came into South Bend undefeated, but blew a 16-point lead to Bob Davie. That hurts. Stoops' next shot Rock's House, and first victory against the Irish, was in 2013. It was also the first Sooners win in the series in decades. Exercising those demons is one thing. Knowing what it's like to win a game at Notre Dame is another.