Director Eli Roth and Keanu Reeves on the set of ”Knock Knock.” (Lionsgate Premiere)

PG-13 horror movies are dead, relegated to a boomlet of here-today/gone-tomorrow shockers in the late ’90s. So, too, are the rash of Japanese horror remakes that followed “The Ring.”

Hard-R horror is dead, having flourished briefly in the years after 9/11, when torture haunted the national conscience. The haunted-house revival has faded slightly as sequels to “Insidious” and “Paranormal Activity” have opened to diminishing returns. And the seemingly unkillable found-footage genre, fueled by cheap-and-easy access to video technology, isn’t the reliable gamble it once was, even though it’s inherently low stakes.

Horror has always been trend-driven and cyclical, with markets for subgenres such as slasher movies spiking in the ’80s, crashing for a period, then coming back in another form. But the genre itself has been facing an existential crisis in the digital age, when most horror movies are either too small to compete in the multiplex or too unsavory to gain footing in the art house.

As viewers have migrated from movie theaters to home theaters, horror has been hit the hardest. An audience still exists for it, but for a handful of prominent exceptions, like the indie breakout “It Follows,” the market primarily caters to video on demand or streaming services such as the new curated site Shudder.

For two years, director Eli Roth has been forced to watch these developments from the sidelines. One of the few brand names in horror, with credits that include “Cabin Fever” and the “Hostel” movies, Roth premiered “The Green Inferno” — his grisly homage to Italian exploitation pictures like “Cannibal Holocaust” — to the lusty “Midnight Madness” crowd at the Toronto Film Festival in 2013. Open Road Films had picked it up for distribution, eventually settling on a release date the following year, but a complicated dispute between Open Road and the film’s production company, Worldview Entertainment, got it pulled from the schedule a month before opening.

Another year later, “The Green Inferno” is finally hitting theaters through an arrangement with Jason Blum of Blumhouse Productions, which has stamped its imprimatur on franchise hits including “Paranormal Activity,” “Insidious,” “The Purge” and “Sinister.” Released under Blum’s new BH Tilt label, the film opened in wide release without an expensive marketing campaign, relying instead on a viral push that taps into Roth’s considerable fan base while eking the most out of modest returns at the box office. (It earned $3.5 million in its opening weekend.) The online strategy seems entirely in keeping with a film that includes the Twitter handle of every cast and crew member in the closing credits. And it also minimizes expectations for the type of extreme horror movie that has fallen out of fashion but has long been Roth’s stock-in-trade.

“The Green Inferno is the pilot,” says Roth. “We’re the test-case release to see if you can make a movie and release it on 1,500 screens, targeting an audience with a digital campaign and directly marketing to fans. So then if the movie makes $10 million [in theaters], it’s a huge hit. You don’t have the pressure of having to make $60 million, because you’re not making movies that are going to appeal to everybody. I’m making something edgy and dangerous.”

How edgy and dangerous exactly? “The Green Inferno” is Roth’s attack on what he calls “slacktivists,” those socially conscious collegians who opine about the issues-of-the-day on social media but approach them with minimal commitment or depth. As punishment, Roth sends a group of them to the Amazon rainforest, where a mission intended to protect an indigenous tribe from developers ends with the same tribe killing most of them and serving at least one for dinner.

“People get involved in a cause in ‘The Green Inferno’ not because they care about saving the Amazon but because they want credit for saving the Amazon,” says Roth, who likens it to the hashtag activism of #Kony2012, #FreePussyRiot and #BringBackOurGirls. “They’re not happiest when they shut down the developers. They’re happiest when they’re trending on Twitter and when they make the front page of Reddit. That’s what I see is going on right now. Everyone’s tweeting the hashtag of the week because they want to look like they care.”

That eagerness to provoke and plug into the cultural zeitgeist has been a feature of Roth’s work from the beginning. “Cabin Fever” could be read as an extended metaphor for AIDS or the SARS virus while the “Hostel” films were his pointed reaction to Bush’s America and its repercussions overseas.

Just two weeks after “The Green Inferno,” Roth returns again with “Knock Knock,” an infidelity-themed thriller, featuring Keanu Reeves, that he made while “The Green Inferno” sat in purgatory; thematically, the film backs right into the Ashley Madison scandal. But while Roth infuses his work with social commentary, he doesn’t care to follow the current whims of genre filmmaking.

“You can’t be conscious of the trends of the day,” says Roth. “You can only be conscious of what’s going on in the world and what you want to see and what you feel there’s a lack of in the marketplace. Haunted-house movies are in right now and some of them are good, but I wanted to make a movie like ‘Hostel’ that’s unlike anything people have seen in a theater before.

“Any time you do something different, there’s always resistance, but generally when you make something original, that’s when people respond to it. You create the trend.”

Between the “Hostel” films, with their implicit critiques of the military torture scandals at Abu Ghraib and Guantanamo Bay, and “The Green Inferno,” which mocks a liberal class of “social justice warriors,” it can be hard to pin Roth down politically. But whatever their merits, his films stand to be fascinating cultural artifacts. Plenty of people will find (and have found) “The Green Inferno” revolting on political grounds or as a simple affront to taste, but even with the two-year delay, it stands to say more about 2015 than any number of its more respected counterparts. And it doesn’t say it softly, either.

“Movies have gotten so safe,” says Roth. “Everybody tries to write characters who are likable, but none of them come off as honest. You have all these movies that read as phony. I never want to shy away from what the subject matter is. I want to tackle it head-on and be unapologetic about it. You don’t want to water down your movie to please everyone. To me, that’s the death of creativity.”

Still, Roth expects some blowback from “The Green Inferno” (and likely “Knock Knock,” too). He seems to welcome it, given how heavily he is gambling on Internet buzz to buoy its prospects. He loves social media and professes a genuine interest in fielding instant reactions and having discussions about the movie. Perhaps his most canny gift as a filmmaker is simply poking the hornet’s nest to see what happens.

“Whether they like it or hate it,” says Roth, “you want to make a movie people will never forget.”

Tobias is a freelance writer.