I share your wish. This project started out because Just is not apt installable. But at a certain point, it became a "just for fun" project (pun intended).
Also, the trade-off here (in my mind, at least) is that you could maintain higher-level Justfiles, but distribute releases containing the portable-shell-script artifacts of said compilation — so that anyone using your package doesn't need just, only a POSIX environment.
For an individual.. if you're happy to install `just` in any place you're going to maintain the project, that seems better.
For helping others use the project, providing a bash script which has all the just UX would at least save them from having to install another tool. (Adds one thing for the maintainer, but saves one thing for others to install).