You're right, it doesn't. It's still a diamond. An artificial diamond, since those are considered "lower quality" for gemstone purposes. Thus, for this purpose there is a distinction between "artificial" and "natural" that matters. Carat for carat, you get more for a "natural" diamond and thus the distinction is useful. Simply saying" but they're all diamonds" ignores this classification scheme, just as ignoring whether a body part is artificially constructed or not matters. But this is an academic distinction anyways since we're at best decades away from pseudo-genetalia that are actually identical to their natural counterparts, and the vast majority of trans people seem to have no interest in actually going through with radical body-altering surgery. But even then, the distinction would exist between "born" and "made" elements, no matter how subtle. Human-made is still human-made - even in diamonds it's possible to tell (man-made diamonds are "too perfect").