Lambda the Ultimate

From machine code to assembly and from that to APL, LISP, Algol, Prolog, SQL etc there is a pretty big jump in productivity and almost no one uses machine code or assembly anymore, however it appears there's been almost not progress in languages for 50 years.

Why is that? Are these the best possible languages? What is stopping the creation of languages that are regarded by everyone as a definite improvement over the current ones?