Branching by cloning was copied from bitkeeper. It was also early git's only branching mechanism. If you listen to Linus's talk when he introduced git at Google

Branching by cloning was copied from bitkeeper. It was also early git's only branching mechanism. If you listen to Linus's talk when he introduced git at Google, you'll hear him conflate "branch" with "clone" because that's what he was thinking of at the time. https://www.youtube.com/watch?v=4XpnKHJAok8 https://www.youtube.com/watch?v=4XpnKHJAok8