Of course, none of this means that there haven't been sex-focused games. They've just typically been in their own cordoned-off part of the industry, rather than on the shelves of your local store.
The first to be treated like a proper game was Sierra Online's Softporn Adventure, an awful text adventure game about a man trying to get laid in a sleazy gambling town. This was later remade as Leisure Suit Larry, although what most people don't realise is that this was more a parody of the original than anything else, and that its designer, Al Lowe was far more entertained by humiliating his new creation than interested in arousing the player at the keyboard.
These early games suffered from the fact that text adventures simply aren't sexy, the graphics of the time weren't up to much, and games themselves were still at a Donkey Kong level of complexity.
Most were less games as interactive versions of a horny, somewhat disturbed 14-year-old's notebook, ranging from Atari games like Custer's Revenge (a naked, erect Custer crosses a screen to rape an Indian maid) and Bachelor Party (a Breakout game with ladies instead of bricks), to PC titles whose names really say it all: Strip Poker (served up in sizzling, sexy… er… greyscale), Astrotit (an interactive discussion of Wittgenstein and how his philosophy relates to the quintessential existential crisis), Drive-In (get to third base at the movies) and Granny's Place (not remotely what you think, but we'd hate to spoil that mental image…)
All these games were from the 1980s, before the PC gaming market really started. After that, developers realised that with the growth of graphics, and the increasing scale of the market, this was the perfect time to establish sexuality as a core part of what mature games could handle, and move the market onto a whole new level of advanced characterisation and social worth.
No, just kidding. They made Sex Vixens From Outer Space, Leather Goddessses of Phobos, Girlfriend Construction Set and Butt-Slam, the PC's only dedicated multiplayer board game about sodomy. Makes ya proud, doesn't it?
CONVENIENT STRAPS: Nice of the mad scientist to put the restraining bands right there. Wouldn't want the poor girl getting embarrassed or anything
Then, as now, anyone hoping for any real excitement from any of these games would have been sadly disappointed. The coyness was already in place as early as Leisure Suit Larry in 1987, where the sex scenes were obscured by a giant bouncing CENSORED box. Others, like Coktel Vision's Emmanuelle, hid the 'good' stuff under incredibly tedious adventure games that bordered on abuse for self-abusers.
One thing that hasn't changed over the years is that sex-heavy games are typically awful. Fortunately, there are exceptions to that rule: for instance, 2005's Playboy: The Mansion is a perfectly solid tycoon game, and Leisure Suit Larry: Love For Sail a fine adventure game, but they're few and far between.
One of the worst ever is the most recent Larry game, Box Office Bust, which features some of the worst platforming action you're ever likely to play, characters who look like they've escaped from your worst nightmares, and hysterically for a game which opens on the line "I'd fuck a cliff", a cowardly lack of even nudity.
It's even worse than the previous low watermark: Lula 3D, because while still unbelievably terrible on every level, at least that one offered some entertainment value by being headfizzlingly insane. Not many games feature random shoot-outs with the police, catapulting dogs at Mount Rushmore, or end with a drugged up pornstar shooting imaginary skeletons with a handgun in the middle of a psychedelic New Orleans.
TRUE MADNESS: We'd show a sex scene from Lula 3D, but they're just too rubbish
Non sex-focused games can still have a little fun, but it's usually more restrained; restricted to the occasional set-piece here and there. Sometimes, it's just to try and set the mood, or when seen early in a game, to try and hint that if it's offering nudity so easily, imagine what might be coming up later fellas if you stick with it.
The random naked ladies at the start of 1992's Rex Nebular and the Cosmic Gender Bender (yes, really) and Les Manley: Lost In LA both pulled this trick. Lost In LA promptly followed it up exactly once, with a truly hysterical 'mud wrestling' scene that barely bothered with the wrestling bit, never mind the mud.
Most never even go that far, if only because games that have to rely on this kind of method for keeping players around rarely have anything else capable of keeping their target audience playing. These aren't great games.