I haven't seen the movie or any images from it but there is a good chance that the women were not actually nude. I've heard that, at least in Hollywood, if a frontal nude scene is in a script, the women may wear a g-string with fake pubic hair to cover genitalia.
As a naturist, I don't quite understand the difference: If someone is watching the movie as a voyeur and believes that the women are actually naked, then what was accomplished by wearing the g-string? Talk about not leaving anything up to the imagination...
For a lot of people things like the slit, the penis or the nipples being visible does make a huge difference between them feeling naked and them not feeling naked. It's cultural conditioning. I've seen several interviews with celebs talking about how they "faked" a nude scene with pasties, flesh colored patches, socks (over a guy's penis) and as a nudist all I can think is "did that few inches of body that you covered really make you feel less naked?"
I've even seen some stuff where celebs talk about having "wardrobe malfunctions" during their fake nude scenes. I remember seeing Brooke Langton talking about her first sex scene on "Melrose Place." That show used pasties over the women's nipples during their frequent behind-the-back/shoulders-up topless scenes that never show the nipple so as not to get into trouble with the FCC. She says that she was wearing pasties, takes her shirt off and managed to knock the pasties off at the same time. She told the story to David Letterman as an OMG how embarassing it was to flash the cast and crew on my first episode when I was just thinking "so you wouldn't have been embarrassed if you had two little caps over your nips but were otherwise exposed?"
Nathan Fillion & Morena Baccarin have a story about how when filming a "Firefly" episode where he appears naked she caused his malfunction. He's supposed to be naked, but really had a sock over his penis. After a take she pulled it off as payback for a prank he had done to her previously. Apparently he went from semi-comfortable wearing nothing but a sock, to embarrassed by that.
Another reason for merkins (that's the term for fake pubic hair patches) is for the sake of ratings and censorship. The horror film "Re-Animator" features a bunch of naked zombies since they were supposed to be corpses in a morgue awaiting autopsy or embalming; which would mean they were covered only by a sheet when suddenly they were brought back. The filmmakers were worried about being given an X rating (same as today's NC-17) if a a penis or slit appeared on screen so they fitted the naked zombies with fake bushes over their crotches.