Because it was probably accidental. As opposed to using something like Lisp macros, where meta programming doesn't require using the type system language and sh

Because it was probably accidental. As opposed to using something like Lisp macros, where meta programming doesn't require using the type system language and shoving it into the shape you need, and is basically normal programming. Now that it's been discovered people are going to rely on the quirks that enabled it, and it's now an accidently designed meta programming language inside your type system. See C++ for why that is bad.