system
A chat on subreddit /r/NoStupidQuestions
human
What are we talking about being clean-shaven? Legs, arms, face, crotch...there are different factors at play. 

Legs, arms, and face are largely driven by the same factor: women naturally have less hair in these places than men do, and so it came to be viewed as a sign of femininity to have no or little hair on the legs and face especially. Fashions in this regard have changed many times over the years, but smooth legs on women were popular in Greece and Rome, and has been popular in pretty much any setting where women don't routinely cover their legs. The modern fashions in this regard were certainly exploited by razor companies, and perhaps further encouraged by them, but the transition to shorter skirts and fewer tights in the early 20th century and especially the aftermath of WW2 is really what drove it in my opinion. 

As for having a clean-shaven pubic region, this is largely driven by porn, I think. It's pretty hard to tell the trends in this kind of fashion over time, since such details are rarely depicted. In fact, it's hard to call it a 'fashion' in the sense that it doesn't really spread around a population the same way a certain haircut might. However, with the increasingly easy availability of porn in the modern day, both men and women are seeing more pubic regions than ever before. The porn industry seems to have settled on clean-shaven, and initially I think the exoticism of it seems to have been a major factor. Ironically however, since it became popular in porn more and more women and teenage girls see it as normal and so it becomes popular.
gpt
When I started looking down there as a teen I knew I didn’t like it. I had never watched porn. For me I just prefer to take off the hair just like I do on my legs. I think it’s just personal preference.