Who says Hodge stays? If Mac is getting a huge bump, I'd expect Hodge and the rest of the staff would too. It's always been a package deal, from my understanding. His staff is his team.
SMU, at least in name, still has 'Methodist' in their name. Whether or not you or I think they have embarrassed/disgraced their represented church, Grant is a Christian and that could absolutely be a draw for him. That said, uprooting from Argyle to Dallas may not be AS far as moving across the country---it is STILL uprooting your kids from their schools and friends. Is he living in Argyle and driving to downtown Dallas every single day and working the long coaching hours along with that? I expect that his better half will have something to say.
End of the day, SMU is a lateral move with potentially better pay if we can't/won't step up to meet it. Hopefully this is a leverage play and we play ball. He and his staff have earned a raise.