Why the PF_SUPERPRIV flag is cleared?

[Parmenides]

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.