He’s probably serious. Craig just watched two much younger guys blow past him at Hayward, with even more clipping at his heels.
His contract with Nike is almost certainly heavily-dependent on performance bonuses. He may be processing a significant pay reduction since he didn’t make the Olympic team. He didn’t make it in 2016 either. If you’re a marquee Nike athlete and you’re not making Olympic teams, your pay is going down.
Another sponsor would probably pick him up since Craig is fun and marketable (Symmonds’s time at Brooks comes to mind), but Craig might not want to upend his life and gamble on a new training situation at this point in his career. His coach is a Nike guy through and through, so he’d need a new group.
As a fan, I hope Craig at least makes a run at Eugene ‘22 but it’s hard to blame him if he decides against it. Life is short, running at this high of a level is hard, and Craig clearly wants to have more fun in his youth than the lifestyle of a globally competitive elite runner allows.