Basically, western stereotypes of asianness are
western social constructs. They're to do with identifying an "other" group. Any character that lacks the "other" signifiers is assumed to be a default. e.g. westerners assume a default stick man is a white male, despite being drawn in
black. Hell, Adria Richards, a hardline feminist
assumed a stick man depicted a male, even though the artist (xkcd) deliberately added signifiers that it was female. When even radical feminists make the assumption than an unlabeled character depicts a white male unless you go whole hog and draw boobs and a skirt on, then you know that these assumptions run deep.
And The Simpsons (not to mention Lego men) are just assumed to be Caucasians despite being yellow, depist a very deep cultural connection Americans make between yellow skin an asianness. When Marge Simpsons, a character with yellow skin and a blue affro depicts a white person an nobody questions that, it makes no sense to demand that asian draw their characters to adhere to
our stereotypes of what "their race" is meant to look like.
Naturally, from a Japanese point of view, westerners are the "other", so they've codified their own signifiers to indicate that. The key thing people don't get is that those signifiers don't correlate to the western signifiers of
"asianness". Japanese have skin tones similar to Americans (japan stretches into snowy regions), they don't codify the world into "white" and "yellow" skin, like the west. It's similar with eyes. "Large eyes" in anime signifies femininity, youth and naivety (baby eyes) rather than ethnicity. Also: hair color. when hair color is used to indicate "being western" it's invariably the "blue eyes/blond hair" combo - the cliche. Mixed hair color isn't meant to indicate ethnicity, but identity.
The Japanese anime cliche of an American is blonde hair / blue eyes and a big hooter. So a Japanese person could complain that American cartoon characters don't look American to them ... The argument is about as sensible as saying "why don't french cartoon characters
look french? I mean hardly any of them have red scarfs, berets and stripy tops".