GSP defended the title for more than 5 years, firmly established himself as the WW GOAT, was clearly past his prime after knee surgery, and had already planned to step away from the sport prior to the Hendricks fight. To suggest that GSP "quit" is just ignorant.
As for Conor, I highly doubt that he's every ducked anyone. I certainly believe that the UFC ducked people on his behalf and paved his way to the belts, but Conor's confidence is genuine. When he says that these guys aren't on his level, I believe that he actually believes it. His desire to fight Floyd has nothing to do with ducking Khabib or Tony. He's simply chasing that paycheck. Any sane person would do the same thing if they had the opportunity to box the biggest name in combat sports for that kind of money. It obviously messes things up a bit for MMA, but I can't begrudge someone for trying to get their money.