The question you should really be asking is why shouldn't they? The best applications out there do one thing and do it well. Awk, sed, vi(m), emacs, git. Need I go on?
Emacs is the polar opposite of the Unix philosophy; it's more in line with the Lisp Machine tradition. Programs like sort, uniq, and grep don't embed interpreters for dynamic languages and provide thousands of different extensions for anything from reading mail to connecting to IRC.