Because those who play the bra board say that they play skateboarding, while those who play the four-wheel skateboard always think that skateboarding should be an extreme sport, including four-wheel skateboarding and snowboarding, both of which are skateboarding, but the bra board is just something invented by sticks for fitness and entertainment, so they don't think that the bra board deserves to be called skateboarding, so they despise those who play the bra board and say that they are skateboarders, which is a stain on skateboarding. There is also some contempt for sticks. Plus, most of the people who play with bra boards are children who are not sensible. When they step on the bra, they still feel how great they are. When you fall on the skateboard, he will step on the bra and laugh at you, which will further deepen the skater's dislike of Braer!