Why Haven't Special Character Sets Caught On?

theodp asks: "Almost forty years after Kenneth Iverson's APL\360 employed neat Selectric hacks to implement Special Character Sets to express operators with a single symbol, we're still using clunky notation like '<>', '^=', or 'NE' to represent inequality and cryptic escape sequences like '\n' to denote a new line, even though the Mac brought GUI's to the masses more than twenty years ago. Why?"