Because just like with many other things humans use the least common denominator wins. Everybody understands the concepts in Java pretty much but having trouble

Because just like with many other things humans use the least common denominator wins. Everybody understands the concepts in Java pretty much but having trouble with LISP concepts. Just by interviewing ~40-50 Java programmers (mostly juniors) I can tell that even concepts like recursion is not well known or understood among them. At this level they think they do not need to know these advanced concepts to be successful as a software developer. As a company you want to use a language that everybody can understand so you do not have trouble with hiring, few exceptions (like Jane Street).