Because he’s getting paid a metric ton and wants to win a title. He wasn’t accomplishing either by staying at ND. He could have leveraged the LSU offer into a metric ton of money at ND, and the SEC is only going to get harder, not easier. He had a better chance at the playoffs playing Purdue and Navy every year than having to compete with Bama, Georgia, Oklahoma, Auburn, Florida, etc. to even win the SEC