Two, cycling jerseys fit snugly and can reduce air resistance. It makes your whole body slippery, like an old mudskipper rolling around in muddy water.
Three, wearing cycling jerseys can make you look more professional, and can compare the aura of a square dancing mom. Everyone thinks you're a professional athlete. Even if you're riding a Phoenix 28-inch messenger bike, you can look like you just came off the Tour de France. Make people doubly feel how awesome your crotch is.