Github shows 98% of code is "Shell" on top of that there are also many different package managers that people use: fnm, volta that are build with rust. You can also install nodejs using homebrew.

>Does nvm not use npm internally?

No. It downloads binaries from nodejs.org. There is no "official" canonical means of managing Node versions. It's just a grab bag of community tools like NVM.

I would dare to say that average person who works with Node does not use nvm.

Really? I think it’s even recommended on the node website’s install page