That's not the reason. lmao They were doubting after that and before that. Conor could've beaten Mayweather and Diaz and they'd still be doubting.
It's not hard to notice that people don't perceive Conor at face value. It's because they hate him. They're jealous of him. Not in the sense of he's riding a Lamborghini that they want, although for some it might be true. They feel he doesn't deserve what he's gotten. They've concocted this false reality where he's this and this, and he's going to have consequences for his actions...and when those consequences don't come it's earth shattering for them. And it only amplifies their envy even more.
The Khabib fight will have a larger effect than any other one on the psyche of Conor haters. Even more than Aldo, Alvarez or avenging the second Diaz loss which I'd say are the current 1, 2, and 3rd place contenders respectively. More people expect Conor to lose than ever before. More people want Conor to lose than ever before.
I say this with true affection, that I genuinely worry about the mental state of Conor haters if he wins. Most will make it by concocting more false realities to help them ease the pain, but I don't feel everyone will make it this time.