I can’t answer for any other female performers (or male or gender neutral performers that may have reason to wear lipstick right up to the sex part of a scene and then remove it) but I can explain my own motivations:

See, the directors want lipstick. I don’t know why. Maybe they think it looks better, maybe they think the consumer likes it better, maybe they just want a defined lip and neither they nor the makeup artists have caught on to this nifty new thing called lip stain. I just don’t know.

I don’t like eating lipstick. I don’t like subjecting my fellow performers in a scene to eating lipstick. I really don’t like a scene being stopped every five minutes so someone can wipe up all the lipstick that’s gotten all over faces, genitalia, and other body parts and then use that opportunity to ”touch up” my lipstick (which really means glob on a bunch more).

So we meet halfway. We compromise. It works.

Personally, I’d still take washed out lips over subjecting the person I’m sucking face with to the waxy taste of lipstick.