Why do mamas boys get teased to much?

My younger cousin who is 13 or 14 and his dad says his peers are teasing and rediculing him because he's a mamas boy. Even a few teachers disrespect him and criticize him and blames him and my aunt for this. They don't baby him. My uncle does NOT like him being a mamas boy. He's trying so hard to get him to not be one. He said, "You watch. You're not going to be a mama's boy when you graduate high school."
My dad was like, "Boy you better stop having mommy drive you around all the time and start knowing your surroundings. It's time to be a man!"