In a lot of Asia, youth is seen as attractive
Human eyeballs are generally all the same size, regardless of skull or body size.
Youth = small
Big eyes and small everything else therefore means cute
Art often exaggerates or interprets
Anime is art
Anime is also not a new medium at all in Japanese, and now global culture, and has had a lot of time to evolve
I'm not defending it, just explaining it, in case people don't understand, because this is a long-standing and very common complaint/criticism