User being unable to decrease process nice value

[Artem S. Tashkinov]

Hello,

I've been unable to find any rational logical complete answer to the
following question.

In Linux non-privileged users are able to increase their own processes
nice value but they are not allowed to decrease it back to 0.

To me this does not make any sense because, even if that's some kind of
very old policy/rule from old UNIXes, the user can still simply restart
their processes to get to the coveted 0.

What's the rationale behind this seemingly illogical and easily
circumventable limitation/restriction?

Best regards,
Artem