I suspect the reason is the same as the use of local git GUIs and TUIs; git has a terrible CLI, so everyone uses its plumbing, but not its porcelain.
It would be funny if I didn't mistake it for an actual git manpage.
The link you posted looks pretty helpful. I guess my needs for "interesting" git operations are low because I've never felt the need to move beyond the CLI. (Mostly, that is. I do click the colored bars in VS Code to stage commits and then commit from the command line.)
Occasionally I need to search for help when I screw something up. More often the solution is in the git warning message ("You need to 'git pull' before you can push" - paraphrasing.)