Earlier quoted context omitted.
For simple projects (like ppl experimenting with git) you will always want to save all changes. So why stage first ?
Not everyone stays a beginner forever, and it's nice to have a tool that doesn't play to the lowest common denominator. It's really not that hard to just do a "git commit -a" if you want to avoid staging.
But the vast majority do, or at best become perpetual intermediates (https://blog.codinghorror.com/defending-perpetual-intermedia...).
99% of developers out there didn't need a power tool for source control (source control is already quite a power tool many devs can barely handle, even in SVN form...), yet here we are: Git is imposed everywhere, with its horrible UX.