(almost) Pure C instead of C preprocessor

Why isn't (almost) pure C used instead of the C preprocessor?

Sure I understand it would be a little more verbose. For example:

#define PI 3.14159

would be written like something like this:

#define PI {printf("3.14159");}

Yes, it's more verbose, but for more complex stuff I think it would help alot. Also, going with this design, programmers wouldn't have to learn another language (namely the C preprocessor) in order to write macros.

So, are there any other reason except the verbosity that the C preprocessor is not just pure C (with perhaps small modifications, like the addition of the define keyword)?