Who knows ... To make us more relatable, or easier to work with, maybe.

[ Because Zero is, of course, being a box of relatability right now. But hey, there's still time to pass before he's done here. He pauses, then decides to give a little more information than what amounts to a verbal shrug. ]

... The first reploid was dug up somewhere, a long time ago. All other reploids were based off of him in one way or another, and he had emotions similar to a human's from the start. ... Maybe moreso than the rest of us.