Learning kung fu or the violin isn't beyond most people either, but I'd rather not have that be the prerequisite for being able to be productive on my team.

Most companies don't prioritize paying a potentially highly compensated worker to learn an obscure language when the job can just as effectively be solved using standard skills and languages that are much easier to acquire(hire).

Also, despite the passionate defence that many functional-first language advocates give, I have never seen any conclusive evidence that these languages, in general, produce better results than the standard suspects.