[Haskell-cafe] Why isn't hsc2hs functionality provided by ghc?

I was wondering today, why hasn't hsc2hs been merged with ghc so that it would be possible to add a {-# LANGUAGE ForeignFunctionInterface #-} at the top of a source file and then load it with ghci or compile it, without the intermediate step of calling hsc2hs? This would be exactly like the CPP extension. I don't have to call cpp manually. All I have to do is to add {-# LANGUAGE CPP #-} and then ghc will take care of the rest. This would also mean that there would be no need to have a separate file extension. Surely I must not be the first person to have that thought, so there must be a good reason why this hasn't happen yet, but what is it?