This is not what people expect, so that's one obvious reason it's very likely the wrong decision. I would have never known this. If you are relying on a public external product on github, you have to go several painful steps to make it 'safe', you have to re-upload it, and there's no good reason to make people do it. It's a giant disincentive to fork things on github. To be safe of finding things later, there will probably be another git repo website that will agree to "host" your forked projects safely, so that you can access them.

I understand on the other side, there's value in being able to stop people who forked your code. But it's a very weak stop-ability, because they could just keep the code locally and re-upload.