Heard an interview with Stormy Daniels where she ran it down.

Back in the day, porn actresses did a lot of touring. They’d do live appearances at topless bars around the country. They’d sell DVDs, sign autographs, etc etc.

In a lot of these towns, the local police would harass the dancers for fun and profit. One of the most wide spread laws was that the dancers couldn’t display any pubic hair. The dancers would shave to avoid breaking the law.

The touring actresses learned this and followed suit. So a lot of porn actresses started appearing shaven. Now the guys who watched the videos saw this and started asking their wives/girl friends to get the shave, too.