Open Home Assistant to other Git repositories in addition to GitHub

Hello, I was wondering why Home Assistant only accecpts repositories hosted on GitHub as this is a Microsoft product.
It is not about talking bad about Microsoft but to talk about adding other repositories like GitLab, BitBucket, Gitea or Codeberg. I bet FLOSS people are interested in hosting their repos out of GitHub only.

As workaround so far, how can one add a repo f.e. from Codeberg to HACS via 2add custom repository"? I did not find a manual right now.

I do not think there is a requirement to use GitHub.
If you read the installation instructions for integrations on GitHub, then most include a section for manual installation, which is not depending on GitHub.
Often there is a section telling that it can be installed from HACS too and that might require GitHub, but HACS is a third party integration and there should not be anything stopping you from making similar integrations for other repositories.

Also Home Assistant is Huge. It is the 2nd largest (by activity) project on GitHub behind VSCode project. Ant Paulus and Frenck are this week are presenting the keynote at the Github Universe event.
There is a good relationship there and very little chance the main project will move.