That’s great for developers who are competent in that paradigm but what about hobbyists or sysadmins who have little interest in software development?

I’m not saying POSIX shells are without fault but they weren’t just created because C is too low level; they were created because people used a terminal who weren’t always techies so Bell Labs created a language which anyone could easily write simple programs with. Granted that need has dissipated a little but your solution of having one language to rule them all creates more problems than it solves (really the only problem it solves is OCD for a few LISP enthusiasts).

The reason there are so many different programming languages isn’t just an element of NIH; some languages do genuinely handle some use cases better than some other languages. Plus there is always going to be an element of user preference. So your idea of a perfect system would be hell for a great many other people - myself included (and I do generally enjoy functional programming).