The same applies to make without arguments though, make what? Grammar / word meaning aside, unknown / missing commands printing the help file or suggestions is a good pattern.
I think it's less grammatically ambiguous with make. It implicitly means "make <the project>". For most projects that's pretty well defined (and also grammatically correct since 'make' is a verb and 'just' is not).
But even so it would have been a better design for `make` to list top level targets or something.