> I've definitely been using .PHONY on various Linux and MacOS computers long before 2017.

Me too, and I've also used Makes which didn't (on e.g. Irix). What I wanted to express had been that you can't even rely on `.PHONY` existing, much less many other features.

I think it's pretty reasonable to expect GNU make to be available, and rely on its features. IRIX is dead for 18 years now.

If I may cite myself:

    Don't forget that not every Make is GNU Make, BSD and other nix like Solaris/Illumos still exist.

And I'm not even talking about Windows and Nmake.

Both BSDs and Solaris provide gmake via official channels.

There is "make" for Windows too, but it's not as relevant - the windows commands are so different, it's unlikely you'll have a cross-platform file for Windows and BSD/Linux, unless you require user to install unix tools on Windows, in which case they will likely come with GNU make.

I think in most cases, using GNU make is the easiest way to provide compatibility with multiple OSes. There are certainly exception - if your daily driver is FreeBSD, use BSD make. But for Mac OS or Linux users, GNU make is a good default.