Fair enough,
Its because real girlfriends not always that attractives & full of flaws,
As we are as men but people that gonna love you still gonna love you despite your flaw in others eye,
So we're never worried of things like that when drawing a character,
That they need to be good or beautifull but more like yes that is nami its enough,
They are the most beautifull in the eyes that loves them as they are,
And it sell well as artwork so its not pretty convincing statement