From the link:

the project does not accept patches from people who have not submitted an affidavit dedicating their contribution into the public domain.

So now I see. Since the project is in public domain there's no copyright/left around it. And if you want to contribute, you need to sign a paper that says you're dedicating your patch to the public domain.

If you want to extend it anyway, you’re basically required to fork I think that's not totally true. Forking is only one of the approaches.

Nonetheless, I had the wrong idea of how SQLite is governed 🤦 Thanks for the refresher and the link 🙏