Pizza Hut's new Grilled Cheese Stuffed Crust Pizza. (Courtesy Pizza Hut)

Call them what you will. A sign of the apocalypse. Unabashed marketing ploys. The anti-kale. However you view the latest splashy fast-food innovations, know this: They're probably not going anywhere. At least for now.

The latest of these creations to be foisted onto America: Pizza Hut's Grilled Cheese Stuffed Crust Pizza, which features mozzarella and cheddar baked into a crust that's topped with bread crumbs and melted butter. Close relatives of recent vintage include Burger King's Whopperrito and Mac n' Cheetos, KFC's Double Down, Pizza Hut's hot-dog-crust pies and Taco Bell's Doritos Locos Tacos.

Such creations, often referred to as stunt foods or limited-time offers if they're temporary, aren't concocted in a vacuum, especially since they can take months or even years to develop. In the last few years, the trend has grown amid efforts to lure customers back into fast-food restaurants, as well as diners' quest for novel items to share on social media.

Now it seems like each release is wackier than the last. "Like clickbait, the concepts are so unbelievable, so shocking, so Onion-headline-esque that they work," said Sophie Egan, author of "Devoured," an exploration of the modern American diet. "They're irresistible."

The wave of headline-grabbing fast-food items has its roots in the recession, when the industry entered a slow-down period that lasted through 2014. "A lot of these companies were trying anything to get customers back" during that time, said Sam Oches, the editorial director of Food News Media.

Ask observers and analysts what particular promotion was the turning point in paving the way for successors, and you're likely to get one of two answers: KFC's Double Down, a bacon, cheese and Colonel Sauce sandwich that used fried chicken fillets as a bun, and Taco Bell's Doritos Locos Tacos. (Not surprisingly, both chains are part of the same parent company, Yum! Brands, along with Pizza Hut.)

Launched in 2012, Taco Bell's Doritos-taco mashup took two years to develop. The fast-food chain sold 100 million units in the first 10 weeks and surpassed the $1 billion sales mark the following year. "The Doritos Locos Taco was a pivotal moment in our brand's innovation journey," said Rob Poestch, Taco Bell's director of public affairs and engagement.

Coming next year: The Naked Chicken Chalupa with a fried chicken shell.

Why do they do it?

The secret behind the success of Starbucks's pumpkin spice latte, and other seasonal products, is less in the flavor and more in the type of marketing the company uses. (Jayne Orenstein,Julio Negron/The Washington Post)

Despite the effort these foods take to develop, most aren't intended to be sustainable as long-term menu additions. "It's almost never about making money off the product," said Darren Tristano, president of the food industry analysis firm Technomic.

In fact, the bestselling items at fast-food restaurants tend not to be the wacky mashups, but the classic offerings -- Taco Bell's standard tacos and burritos, for example.

The point of the limited-time offers, as Taco Bell's head of social insights, Ben Miller, told the Atlantic, is "getting people in the door." Tristano also said it's about taking money away from competitors and making companies seem innovative and appealing.

So why do companies need to invent excuses for you to come in? The main reason is competition, and not just from their immediate fast-food brethren. Fast-casual restaurants such as Cava Grill, Chipotle and &pizza have moved in on the fast-food market and are growing at a faster rate, said Elizabeth Friend, a Euromonitor International strategy analyst. From 2014 to 2015, fast-casual brands grew at a rate of 10.2 percent, compared to 3.1 percent for the rest of the fast establishments.

Years ago, a diner's only option for getting food quickly was the local drive-through. Now, "It's really easy to get food quickly with minimal effort," Friend said, pointing to such delivery apps as UberEats and GrubHub in addition to grocery stores with hot bars and prepared food offerings.

"Convenience is a very strong factor," Tristano said. And if fast food isn't as convenient as other options, then brands have got to think of something else.

A crazy fast-food item might be the only nudge a diner needs to walk into a Taco Bell or Burger King. If they've seen news coverage or a post on social media, the restaurant might later be at the top of their mind when they're trying to decide where to go.

Why does it work?

No doubt the visuals are especially compelling and share-worthy, which says as much about consumers as it does about the brands hawking them. "The vast majority of us, we don't have a lot of exciting things that happen to us" on a daily basis, said Brian Wansink, author of "Slim by Design" and the director of Cornell University's Food and Brand Lab.

By trying one of these flashy foods and photographing them, people are showing that they're willing to try something new. And like most food photography, those social media-friendly images are aspirational. They aren't usually representative of our diet, a cultural disconnect that Wansink, in a study of historic paintings, has shown goes back well before the advent of fast food and the Internet, let alone cameras.

The whole experience suggests that consumers are full of contradictions. We make an effort to eat well but still want to reject the health-food guilt, at least once in a while. "We want to feel that we've treated ourselves. We want to feel that we've experienced new life experiences, and food is part of that," Egan said.

Diners are also downright curious to know what something new tastes like, which may be more human nature than food culture. "You just can't help yourself," she said.

So what's next for stunt foods?

As long as people keep paying attention to them and talking about them, the short term expectation is that they'll become "increasingly outrageous," Technomic's Tristano said.

In the long-term, though, the "the tide of consumer empowerment" (see: nutrition labels, the fight against GMOs, etc.) is turning, and people may begin to call these foods out as, well, stunts.

The feeling is that "it will no longer be smart business to rely on stunts, and instead [companies will] start to take more of the cues from what these fast-casual chains are doing," Egan said, referring to fast-casual's more customized meals, upscale decor and values regarding the environment, sourcing, health and social issues.

Or they might try stunts of a different sort.

After all, Pizza Hut did recently reveal a turntable pizza box.

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