That's missing my point. What I mean is that where GNU tools are installed, they are a constituent part of the operating system as opposed to running on top/despite the OS. I never said it runs on all operating systems or on all *NIX operating systems.

I'm saying that GNU runs on nearly all unix-likes - for ages, the first thing many admins would do after installing HPUX or Solaris was to immediately install GNU's tools because they're so much better than the ones built into the OS. In that case, GNU tools are installed, but they are not "a constituent part of the operating system" because they are running on top of the OS. Linux distros are unusual in that Linux is just a kernel, so GNU tools were frequently promoted to become part of the core OS there, but out of all the platforms that GNU supports that's almost the only one where they're part of the OS proper. Android then represents a kind of funny regression because Android ships without GNU tooling (instead relying on toybox for coreutils and bionic for libc), but you can once again add GNU tools on top of the OS in the form of Termux, which carries on the long tradition of being far more usable than the OS vendor default tools.

EDIT: Changed "the only one" to "almost the only one" because I remembered that HURD exists and probably also uses GNU tools as part of the OS.