We males can only guess at what truly motivates a woman to display a smooth pussy at a nudist club or resort, but I like to think that she may get turned on by the idea that the men can see her sexual areas completely bare.
It should also be taken into account that a lot of women enjoy the sun on their pussies. A girlfriend I had who would normally fall into the very shy category told me that the sun on her pussy made her wet and she would lie on the beach with her legs open.
There's that too.
The first time my wife sunbathed legs open, we were at a nudist venue by ourselves and I "challenged her" to tan "fully exposed." She decided to accept my challenge; bending her knees to place her feet on the lounge chair, and letting her legs swing wide open. She got so comfortable that she actually dozed off.
While she was asleep I took a peek; and saw that her pussy was opened and seemed moist. When she woke up she noticed it too; and I asked her about it.
She said that being spread open had stretched and relaxed the muscles in her pussy, causing her vulva to open and the clit to be exposed. The "tickling sensation" from the sun and the breeze on her open pussy had clearly aroused her. She was actually quite happy with the experience lol!
She won't do it around other people though, even though she'd very much like to tan that way. She feels that people seeing her wet open pussy up close is "too much"...