I'm not much of a book or art guy but lets go with it.
You named A big popular book that is about sex, is there any others? Don't say the Kama sutra.
Art, well a lot of sculptures and paintings have the odd boob, the occasional dick but there are millions of pieces with no such thing. Just random bits of scenery, boats, portraits etc
Movies imply sex, they always have a hot passionate kiss, then waking up the next day with underwear on. Unless you're watching love and other drugs or a porno.
Games, holy fuck knuckle Batman! The it's like a nudist camp, woman only! Mass effect 2 you meet Jack who is wearing nothing but belts to cover up, how many in game shots of Ashley's ass do we need? Dragon age, Morrigan is wearing a red shredded top and bikini, the obvious suspects like Bayonetta, lollipop chainsaw (which even had an achievement to look up her skirt) and dragons crown, think of all the female characters in fighting games and loads more.
There are a handful of females who aren't rocking underwear as casual dress.
Imagine playing a game, you play as a guy who muscular as all hell, no shirt, tight speedo's so you can see the outline of his junk ... maybe a cheeky testicle popping out the side, would you play that game? You can make your guy look like that in "Loadout", you can even make him butt naked with his impressive member blurred out, so he runs around the battlefield wearing nothing but a grimace!
That game wouldn't sell at all, it would be surrounded in "omg, it's so grotesque!". Gaming is still a boys club and they market it that way, to there junk.