While you're technically correct, what I gathered from their experience is the consistency of usage, between not only their own projects but third-party projects too.
They could make technical improvements to their own Makefiles, sure. But it's more about being able to enter a project and have a consistent experience in "getting started".
We are not arguing whether not declaring phony targets is worse than using comments in `package.json`?
But anyway, comments in a Makefile or `package.json` are not documentation anyway, that's what the `README` or `INSTALL` (or whatever) is there for (in projects like the one the Makefile is written for).
They could make technical improvements to their own Makefiles, sure. But it's more about being able to enter a project and have a consistent experience in "getting started".