Since it's not possible to delete a user but only deactivate them, I want to delete the entire Trailhead Playground and Developer Editions I don't use anymore in order to free some of the usernames I want to use in other instances again, but cannot find an option for deleting playgrounds or DEs.
I can only disconnect them from my account, but that would not free the usernames I used in the Playgrounds and DEs.
Is it even possible to delete the instances at all? If not, what's the idea behind it, keeping all the data trash alive that nobody needs anymore (i.e. instances that were used for the learning paths).