That's because they are stupid. A lot of MMA fanboys hate Nickal because he said he's a better wrestler than Khabib. Guess what? Bo IS a far more accomplished wrestler than Khabib ever was. A lot of MMA fanboys hate Bo because he said he was a better wrestler than Jon Jones. Guess what? Bo IS a lot better wrestler than Jon Jones. Some MMA fans hate Bo because he said he'd be able to whip a chimp in a fight. Now the fact is that chimps have 30% more power than humans per pound. But Bo is 100% bigger than most chimps and is probably 50% stronger than an average human (at least) and would outmuscle them, in addition to having actual technique. Chimps are overrated.
Bo is confident, and should be. He's a tough go in MMA. He's the best college wrestler to take part in the sport so far, and he's always trying to learn more stuff.