It's similar to a honeypot - we put the category
there, hoping people
are honest enough to use the category to make it easy to come along
later and delete them.
a) The people that would be categorising them would likely be people
that could just delete them (or tag them for deletion) if they knew
they weren't allowed.
b) Creating a category for them makes it look like they are allowed,
which will probably just increase their usage.