I don’t know that there’s a particular name for that technique. But you can dissect it and understand why it would be appealing. If I show someone who is morbidly obese and you are just overweight, it says “hey, it helped this fat guy who is far worse off than you, so it can help you too”, plus any image that is unusual will call attention to itself. By saying it is this “one thing”, it makes you think there is an easy solution to your problem, which people like to hear. Think about things you click in general, and you’ll see you are more likely to check something out if it loads quickly, is easy to understand, and requires minimum commitment on your part that is “low risk”. I might have a ten page story that is hilarious, but that will take you a few minutes to read, versus that funny GIF of a cat dancing around you could click instead. And if it’s “one thing”, well how hard is that to remember? If I told you “just do these 37 things in this exact order to lose weight”, then that doesn’t have the same attraction. You’ll have to write that down and you might be reading this on your phone…I see these same adds with some photoshopped ape of a bodybuilder, often with Matt Damon’s head on it for some reason, that say you can built muscle with “just this one trick”.
I’ve often joked that when you click it, it should say, “exercise more, eat better, and eat less of it”. Isn’t that the basis for every diet book in one line?