Why the PF_SUPERPRIV flag is cleared?

Hi, When forking a child process, the copy_process() function will by default clear the PF_SUPERPRIV flag, which indicates whether a process use superuser privileges. That means a superuser process will create a child process does not has superuser privileges. I think the child process of a superuser process should also be a superuser one, while the child process of a normal process by default should also be a normal one (except that the setuid bit of the child executable is turn on). In both cases it is not necessary that the PF_SUPERPRIV flag to be cleared. So, I wonder why the PF_SUPERPRIV flag is cleared by defult.