Oh, please. Ryan retired from politics because he didn't want to risk tarnishing his career by either associating too closely with Trump or making an enemy of him. Like any good Objectivist, Ryan's first priority was his own bottom line, and that's why he figured he'd be better off avoiding controversy altogether and enriching himself in the private sector instead.
And if I sound too scornful, I should stress that that's fine. If private companies think it's a good use of their money to offer Ryan a huge salary in exchange for the honor of officially listing him as a member of their board of directors, more power to him for the easy gig. But it wasn't an act of courage or integrity to retire from politics and quietly farm out his name to the highest bidder. It was an act of pure self-interest.