[jefftk]

Which also shows the right way to delete a private repo if you want people to be able to keep their forks:

If a private repository is made public, each of its private forks is turned into a standalone private repository and becomes the upstream of its own new repository network. Private forks are never automatically made public because they could contain sensitive commits that shouldn't be exposed publicly.

If a private repository is made public and then deleted, its private forks will continue to exist as standalone private repositories in separate networks.

But I agree this is confusing.

[kadoban]

The right way is to make it public first? That's insanity. Making a repo public just to delete it would be a huge information leak even if it was short in duration.

[Ennea]

Just force push something very empty to it before making it public. One more step, yay..

[account42]

So they did think about this use case (deleting a private repo without deleting forks) but did not bother implementing a proper choice for the repo delete flow?