I don’t know exactly when it started. I know my mom shaved her bikini line and trimmed the hair. I don’t know if my grandma did. I’m pretty sure my grandma’s bathing suit had a small skirt? I’m not 100% sure that was always the case, my memory isn’t clear when I was very very young.
I think some of it has to do with fashion. When I was a young teen French cut bathing suits became very popular. A lot of times it is men designing the fashion.
It wouldn’t surprise me if porn led the way for removing almost all, or all, pubic hair on women. Then men ask women to do it. Then women start to accept it as a norm. Then they themselves actually prefer it.
I do think men favor features that make women appear more youthful. Rounder face, fuller hair, longer hair, and thin body, but with curves.
My MIL just told me a story about how angry her husband was that she shaved her legs when they first married. I’m not clear if he was ok with it when they dated.