Early versions of C date to 1972, while early versions of C++ (called C with classes back then) date 1979, only 7 years later, probably a few rooms down the hall from where C was originally developed.

True, templates came much later, but by then C++ was already hopelessly unparsable by LALR(1) parsers. But in truth, it was this way from moment 0, since it was based on C-syntax. Making it parsable by yacc was a lost cause, since yacc followed C and not the other way around.