Something is amiss at the Oscars of porn. More than 100 awards were given out at this year’s show, held in mid-January at the Hard Rock Hotel and Casino in Las Vegas, including those for Movie of the Year, Best Comedy, and Best MILF Release. But careful viewers might have caught a snub that went unnoticed in the adult press. For all its cheerful inclusivity—the show celebrated even more obscure achievements, such as Clever Title of the Year (Cirque du Hole-A)—one genre was left out in the cold. The 31st annual AVN Awards had no “Woody” for 3-D porn.

This marks a major shift in porn, if not for 3-D as a whole. It wasn’t so long ago that insiders believed the new technology would be the savior of an industry under siege from free competitors online. The optimism had its start in early 2009: With Avatar on its way to making billions, the San Fernando Valley mobilized for hard-core depth-sploitation. The director of Caligula—the notorious erotic film from 1979—said he was working on a 3-D sequel. One producer started selling stereo-pornography in a package deal with brand-new 3-D TVs, and another started shooting interactive 3-D scenes for viewing on your home computer. (Even Quentin Tarantino had talked of making 3-D porn.) Then in September 2010, Hustler put out its own big-budget, extra-blue version of Avatar—a sexed-up adaptation with naked Na’vi called This Ain’t Avatar XXX 3D.

Also in September, AVN announced a brand-new category for its awards show: Best 3D Release. “Adult movie production may never be the same again,” wrote adult-industry reporter and erotic 3-D photographer Mark Kernes. The Avatar parody received the first of those awards in January 2011, and a follow-up by the same director, This Ain’t Ghostbusters XXX 3D, won the 3-D prize in 2012. By 2013, though, Best 3D Release had been relegated to the list of additional awards given out on a different day, like the technical achievements at the real Oscars. (“If you even make a 3-D film, you’ll get nominated,” Kernes told me at the time.) By this year’s ceremony, the prize had vanished altogether.

“The main problem is there aren’t a lot of 3-D TVs out there. That’s the biggest hold-back,” Kernes argues. But there are other problems, too. For one thing, the studios had convinced themselves that 3-D DVDs could not be ripped and spread online. Having lost half its business to freebie websites since 2005, executives sought safe harbor in a new video format. But content pirates were not deterred. “The way it was sold to me is that you can’t torrent a 3-D movie,” says porn journalist Gram Ponante, “and of course that’s not true.” Shooting on This Ain’t Avatar took a full week, more than twice the time it takes to shoot most conventional sex films, but the movie sold just 6,000 units, Ponante says, barely enough to make back its production costs. (Ten years ago, the best-selling porn films would sell about 60,000.)

The same occurred in mainstream soft-core. In 2010 Piranha 3D made a $60 million profit on topless ultra-gore and a dismembered penis flying off the screen. The sequel, Piranha 3DD, was released in 2012 and grossed just $375,000 in the U.S. An erotic import from China, 3-D Sex and Zen: Extreme Ecstasy, got lots of credulous press in 2011 for being the “world’s first ever 3-D porn film” (it wasn’t), but failed to sell that many tickets. And last week saw the release in theaters and streaming video of the latest tent-pole 3-D smut: Nurse 3D, the story of a man-killing, girl-kissing, clothes-not-wearing serial killer whose exploits are somehow neither sexy nor fun.

Why is 3-D porn so unloved? The format has long been embraced by films that traffic in sensation, and are more or less indifferent to character or plot. (“Thrills, chills, a lot of dirt,” to steal a slogan from a 3-D horror classic.) Yet what success it’s had hasn’t been so dirty. Data from the MPAA suggest that moviegoers under 25 see twice as many 3-D movies as the rest of us, a fact that seems self-evident when you look at what’s been made and what’s now in production. Most 3-D films are geared toward brains that haven’t yet developed: popcorn action pics (e.g., Need for Speed and Godzilla) and kiddie fare (e.g., Rio 2 and Legends of Oz). Thrills, chills, and some animated parrots.

Thirty years ago, trash auteurs were already lamenting the medium’s starchy fate. The 3-D revival in early-’80s horror and sci-fi was disastrously annoying, wrote John Waters in a 1983 cri de coeur for American Film. The gimmick would be much better used for smut, as it had been in Andy Warhol’s sex-filled Flesh for Frankenstein and the hard-core 3-D pictures of the ’60s and ’70s. “Porno, finally, is the only genre to demand the third dimension,” Waters argued. “Remember The Stewardesses? Huge breasts spilling out from the screen. Or Heavy Equipment? Gay male porno with, well, life itself gushing into the audience’s lap.”

3-D porn had begun much earlier, though. As the late Ray Zone describes in his book 3-D Revolution: The History of Modern Stereoscopic Cinema, naughty stereographs were common in the 19th century, and their popularity lasted for 100 years. In the 1890s a gentleman could look at 3-D scenes of women falling off of bicycles, their skirts scandalously aflutter. In the 1940s former silent film star Harold Lloyd started taking thousands of 3-D photos, some nude, of stars like Jayne Mansfield, Marilyn Monroe, and Bettie Paige. (These were finally published in 2004.) And as 3-D films took off in the early 1950s, so too did randy 3-D shorts. A sleazy 1952 feature, A Virgin in Hollywood, had two 3-D inserts—“The Blonde Slave’s Revenge” and “Madonna and Her Bubbles.” The latter is more engaging: A blonde in black knickers and a diaphanous skirt blows bubbles in the air and bats them girlishly toward the camera so they’re popping off the screen. Even Francis Ford Coppola shot some 3-D “nudie-cutie” color inserts in the 1960s.

The Stewardesses, an erotic 3-D meditation on the subject of stewardesses, was a major hit when it came out in 1969. More explicit 3-D productions followed, notably from a pair of filmmakers, Steve Gibson and Arnold Herr, who’d been doing soft-core stuff till then. “There was this moment where everything kind of shifted,” they told Ray Zone in 2010. The porno theaters in Times Square started showing hard-core films, so they changed their style to meet demand. Since they were shooting in 3-D, they exploited the effect as much as possible. “Things would just hang out of the screen. They would hang there, legs, arms, genitals,” said Herr. They also used the pop-out for the culmination of a scene, what they called the “wet shot.”

Could that be the place where 3-D porn went wrong? According to the eww-theory of its recent failure, no one wants to see negative parallax in a sex scene. At a porn industry event in 2012, one executive worried that “the things that can come at you are the things that a male viewer does not want coming at them.” Indeed, the major 3-D porn releases of recent years have been somewhat conservative in their use of the technology. There’s very little pop-out in This Ain’t Ghostbusters or This Ain’t Avatar, in fact. “They’re mainly using 3-D to increase the depth of field, kind of like the real Avatar,” says Gram Ponante. “It’s being done in a non-exploitative way, which is strange for porn.”

Or maybe it’s just an extension of the problem that has afflicted all kinds of 3-D from the very start. If the medium is slowly dying, it’s because no one’s yet decided what it is or where it fits. As a schlocky gimmick, 3-D is too hard to implement and too expensive to produce. As something less obtrusive, like a better version of HD, it’s not been distinct enough to win an audience. 3-D porn is caught between these two extremes, self-conscious and uncertain of its own identity. You can see this hesitation in the 1977 3-D hard-core film The Starlets, where a young actress pays a visit to a casting director. He’s got a pair of red-blue glasses on, and he’s watching 3-D porn when she arrives—a 3-D-porn-within-a-3-D-porn. “That’s one of our new training films,” he tells her. “It’s pretty far out, isn’t it?”

“Very impressive,” she says, reaching for his fly. “Can we go on watching while we rehearse?”

“We’ll just start easy, towards the screen,” he says. They’ll have to do this very carefully. 3-D sex can be confusing.