I'd say the facial features are more about relatability than neoteny.
Big eyes are expressive. Compare an American comic book to a Japanese manga. In the latter, you always know exactly what a character feels, even when they're making a very subtle expression, while in the former, you can only tell in close-ups, and even then it's never as vivid as it would be in a manga.
Simplistic facial features make something easier to relate to. Anyone of any age and any race can project themselves onto something with very general or abstract traits.