GSP was not even interested in defending a title in the first place and getting back into the same pattern as the one that made him take a break from the sport 4 years ago. He kept saying that BEFORE he made a comeback. He was clear that he was interested in super fights, or legend fights. He was just true to his word. I don't believe he is afraid, besides about those health issues stemming from his mass-gaining process. Caring for your own health is pretty legitimate, honestly.
Keep calling him "scared", a "pussy", or whatever...when a match against Conor McGregor that will make both men tens of millions of dollars is inked, we'll see whether he was scared, or just smart.
I can guarantee this is the match he is aiming for since he ever considered coming back.