About being chibi... its usually made in that style because of what Alex said but he missed one important piece, normally this is used on games where you customize (add clothes to base) so when animations are involved each piece of cloth need a frame too, so its easier to do smaller chibi look like doll (Yes Helm they are called dolls too...) than making a big realistic base, since it would use more work to animate and that is = to more frames for clothes....
Sooo resuming people who do them usually are lazy guys
Jk its just that players accept chibi so well, so why bother making realistic???