Why would you ever use a language which isn't C? All you will ever need is C. Everyone knows it, and it can run on everything. Why use some stupid hipster language like LISP or Haskell? Just accept C is superior.
Also, widely used != quality, look at COBOL, look at Java, C is no exception. It's just too much work to replace it at that level, it would completely fuck up the compatibility with other systems, especially if you want to do things good and make it impossible to implement a POSIX layer on top of your system.