>>103932469While they really don't know how it works, Japanese idea of character design isn't always the same as how we see it. For example, a heroine in light novel may have black hair, but on the cover illustration you see her having red hair. It's because the reader will immediately know that the red hair means certain type of character (hot temper and maybe tsundere personality). Mostly it's to draw attractive characters that also send message that this character has this type of personality.
You also see anime characters that are supposed to be fat, but they don't look fat. This is because too fat character just isn't very cute, but also because fat character design is often associated with selfish/evil traits (of course there are exceptions) and you don't want to send that kind of message when your character is not that type of person.
