The @conservancy resource page, GiveUpGitHub, has stood for years as a great clearing house of reasons why, and how-tos for those wanting to leave the enshittified platform.

This blog post explaining why the Zig programming language has gone full #GiveUpGitHub gathers a lot of great explanations why everyone should, and how they did.
https://ziglang.org/news/migrating-from-github-to-codeberg/

Some of those might even be good to update the SFConservancy resource page.