Could be I live in a bubble, but I don't use git because of GitHub or with GitHub that much. No doubt, GitHub is/was great for distributing software but I feel we'd still all be using git without GitHub

Practically no one was using Git before GitHub (except Linux). Subversion was much more widespread.

Subversion was (and is) an admirable project, and filled a void by being much better than CVS.

When I discovered git, I couldn't go back to svn - git fit my mind _so_ much better.

It might not have seen the meteoric rise without GitHub, but just like it's weird to find servers running an OS other than Linux these years, I suspect there would have been a steady growth that eventually made it dominant.

I suspect it will be very hard to unseat git at this point - for all its untuitive UI it's good enough for most things, and it's been slowly improving for the use cases where it's weak.