This 2007 talk [1] of Linus Torvalds promoting git to Google was how many people were introduced to the concept of git in those days before GitHub, I remember watching it myself. Emails requesting other maintains to pull your branch was very much the suggested workflow around git.

And it was actually part of git. Even back in 2005, git included a script git request pull that generated these pull request emails. I'm pretty sure people called these emails "pull requests" before GitHub came along.

[1] https://www.youtube.com/watch?v=4XpnKHJAok8

git request-pull is.