There's been a bit of a furore in the emulation community lately centred around the PlayStation 1 emulator DuckStation, which has now seen two license changes recently.
The problem from the article is that the GPL was violated and somewhere downstream the user demanded they fix something to upstream. Being that downstream has modification without being published (my assumption on the GPL violation, either found due to inconsistent bug reproduction or other), the author is understandably upset.
The article says he got permission from people who wrote the code to change the license. If they didn’t give permission then he has rewritten the code.
They usually do this if the project finds out it's being used in some uncouth way and don't want to be tied to whatever that is - limiting their exposure and liability, essentially.
I imagine they found some cheap hardware vendor selling this on their shipped units on Amazon or something and don't want themselves tagged onto a lawsuit about it. Probably got wind of some legal action coming in the future.
It's called a CLA. Nearly all of the Linux Foundation uses it.
Edit: As said in the article, apparently the DuckStation maintainer painstakingly replaced every piece of GPL-licensed code instead of using a CLA, which he was aware of. Props, I guess.
He specifically said he is against taking copyright away from the developers that wrote the code. The way you commented on the CLA issue reads as though you intentionally left this part out, as his legitimate reasoning for it would go against your views on the matter.
Please accurately represent the people you are quoting next time.
Forks are used by developers to not only "fork an application", but also just to fork the repo, work on their own branches, and push (PR) them back to the main repo. I have forks of many repos, but that doesn't mean "i have forked the application under a new name".