I agree that git doesn't strictly enforce a team workflow, but 'pull requests' predated github and many use a pull request based workflow without github. Having a local fork, a remotely accessible fork, and asking the repo maintainer(s) to pull from your remote repo to merge into the release repo doesn't require github and many projects use that structure without using github at all, most prominently, the linux kernel. `git request-pull` is a built in command after all.