I don't think it will be to do with not being able to make it at the top of the game, he's only 25 and was getting better. No reason to think he'd peaked, spinners especially seem to get better with age. Unless the injury is a career changer, could be.
My guess is that he's got an offer from somewhere that's just too good to turn down, and it's now or never. Double first from Cambridge, plus a Master's, he'll be raking it in whatever it is he does. Nice position to be in all told, choosing between those two options. When I was 25 I was choosing between accounting and a different kind of accounting.