http://www.sequentialtart.com/archive/dec03/ao_1203_3.shtml#:~:text=Japanese%20history%20professor%20and%20anime,artistic%20conventions%20established%20by%20early

Japanese history professor and anime expert Antonia Levi, author of Samurai from Outer Space: Understanding Japanese Animation (Open Court, 1996), concurs with Schodt's view that the oversized eyes and generally Caucasian appearance of many anime characters stems from the artistic conventions established by early shoujo (girls') manga. However, she proposes a more specifically sociocultural explanation for how this came about. According to Levi, when the first generation of women manga artists took over the girls' comics genre in the 1960's, they wanted the option of doing storylines with more action and plot development than the stereotypically sugary, sentimental romances their male predecessors had assumed young female readers would prefer. However, since it was still socially impermissible for female characters to do anything particularly unconventional or adventurous if the story were set in anything resembling contemporary 1960's Japan, the female manga artists of this pioneering group resorted to setting a far greater proportion of their stories in Europe and the United States than their counterparts in shonen, or boys', comics did.

It was a roundabout way to do female stories that dealt social taboos. The look of the characters stuck as a result. See: Anime's Obsession With Europe: A Brief History