The only people he remotely owes anything to are his teammates. Do you know how banged up he is? Do you know if he talked to the coaches and his teammates? Do you know how they feel about him sitting? I'm guessing the answer is no to all of the above.
The optics only look bad to people that don't understand that college football is a business. Coaches take other jobs and don't coach the bowl game every year, nobody says anything. But heaven forbid a kid looks out for his and his family's future. Tell me, if Fournette plays in the bowl game and suffers a career ending injury, is the university going to take care of him and his family like saving himself for the pros will?