Uncanny Valley: https://en.wikipedia.org/wiki/Uncanny_valley

tl;dr: Neither regular, boring, human faces nor highly stylized comic / chibi / animated human beings are percieved as "inhuman", but as soon as an artificial face looks too real but still slightly off, basically the middle of the scale between "real" and "definitely man-made", it can provoke feelings of extreme discomfort in the viewer. You're basically creeped out by something that tries to look human but fails at that only barely enough to notice.