Because he’s about as game as it gets. The only fight he ever “turned down” was a one day notice rematch with Michael Johnson, when they told him the fight would no longer be for a belt and they would be paying him less than originally. I’m sure at this point he just wanted to fight and get paid. He’s getting older and had been in camp forever. His fight with Khabib just got cancelled for the 5th time and he’s probably never going to get a money fight with Conor, whose already ducked him before. You can’t just keep waiting on these fights forever. Especially at 36. Given the circumstances on the line and the opponent, it was probably about the riskiest short notice fight ever taken, and he paid the price for it. But it is what it is.