I never thought that old organization names became available on Github. After a merge makes sense to keep them locked again or pass ownership to the new owner, not let anyone create that under the old name.
Is there a particular use case it works this way?
That said I doubt this affects millions of orgs, are organization renames that common?
The problem is that people ever bought enough gold to cover costs.
Admitedly, its also reddit problem that they went from hosting links/text to also hosting images/video which is a completely different (and more expensive) beast.