Earlier quoted context omitted.
You're not accounting for updating my hundreds of existing Makefiles and CI config, and asking users to install yet another build dependency.
If it's hundreds, I'll agree with you, obviously that would be a huge effort to migrate. But you made the argument that adding another build dependency is somehow difficult or undesirable which I can't see; the tool is installed in seconds on all major OS-es and package managers. So let's not conflate those two separate things, yeah?
just doesn't even do many of the things make does, as the README states: "just is a command runner, not a build system"