The main use case of a shell is interactive use. There is no reason to invoke a teanspiler when you type a command to be immediately executed. Often its syntax is a bit awkward because in needs to be compact and quick to type.

If you want a better language for complex scripts, use Python, or even Perl, they are now ubiquitous, or bring someting self-contained like Lua or Janet with you.

It would be great to have a different ubiquitous shell language on Unix machines, but it's unrealistic now.