This is typical Go design, other languages do it worse, it isn't really needed, and then it gets added half way as it was supposed to be if done early on, and everyone cheers how Go is a "simple" language.
Just like some other famous languages of the authors.
It's abject hackery because such "comment" directives don't even necessarily have to be a comment to be active:
const x = `This whole thing is
a
//go:generate worse-is-better
multiline
string literal`
A lot of people in this discussion are beating up Go for using syntactical comments for directives, but in reality the implementation is even less principled than that!
Just like some other famous languages of the authors.