I believe that Git is decentralized. Because people choose to use Git hosting services doesn't make Git itself centralized. Git doesn't force you to sign up on GitHub, GitLab or Bitbucket. You can use git-appraise to get decentralized code reviews. You can use git-bug to get decentralized issue tracking. You can always send maintainers patches with the built-in send-email command as GitHub/GitLab/… require an email address either way. You can always clone and push the repository somewhere else. Most (self-hosted) Git hosting services provide an automated migration procedure for issues, discussions, etc.