I find it a bit amusing that Gitea does not use Gitea to develop Gitea. Does anyone have insights on why they chose to use/stay on Github?

Dogfooding is an excellent way to demonstrate a product. I wonder how many OSS (and commercial) projects actually do this?

Onedev ("Self-hosted Git Server with Kanban and CI/CD") specifically states that they're doing this: https://github.com/theonedev/onedev