The Western world has become obsessed with NO SPOILERS since sometime in the 1990s.
When exactly? Hard to tell, but there was a 1991 episode of the Simpsons where, in a flashback to 1980, Homer is leaving the theater after seeing The Empire Strikes Back and blabs that Darth Vader is Luke's father, angering the people in line who haven't seen it yet. I'm almost certain that was projecting the mindset of 1991 back onto 1980, since you didn't see any comedy sketches, movies, TV shows, etc., from the 1980s that assumed a NO SPOILERS attitude among the audience.
Then in 1992, The Crying Game derived its popularity from its spoiler-able ending, where a chick is revealed to be a dude. Again you didn't see that in the '80s. In the slasher movie Sleepaway Camp, the killer is a female character who turns out to be a boy. A more popular thriller, Dressed to Kill, also had a transvestite slasher whose identity is revealed in a shocker style ending.
Yet as far as I know, people who liked horror and thriller movies -- basically everyone back then -- didn't throw a temper-tantrum if somehow the ending were leaked to them before seeing or finishing the movie. If that mindset existed at all, it was so uncommon that no one else in the culture referred to it, as The Simpsons did in 1991.
Even video games have become infected by NO SPOILERS. I only rarely play them anymore, but I do keep up roughly on the state of the video game world, and it amazes me how psychotic people are about not learning any plot details.
This is a radical change from even 20 years ago. In Metroid, an incredibly popular game from the late 1980s, you controlled a space hero character hidden under a suit of armor. If you beat the game, the armor came off to reveal a woman, unlike what you'd expected. Most kids did not beat the game, so when they found out, it should have triggered their NO SPOILERS alarm. But back then people were not as autistic as now, so none of the millions of kids who played Metroid curled their toes when they learned what the shocker ending was before finishing the game for themselves.
What is the best way to view this shift? Before, consuming a work of culture was about getting absorbed in some other world -- connecting emotionally with the doomed crew of Alien, feeling transported out of your body at a New Wave dance club, or visually exploring the sublime far-off worlds of Star Wars. Because it was a personal, visceral, and emotional reaction to watching the movie or hearing the song, only the movie or the song itself could give you this desired experience. Others could try to tell you what it felt like, but it never came close to the real thing. Emotional responses cannot be spoiled.
Unlike emotions, communication through language is not an intensely personal experience. Indeed its impersonality and abstractness is what allows us to convey ideas so easily to scores of other people far removed from the topic of conversation. "Kimberly went out on a date with Joey" is not one of those you-had-to-be-there kind of things. It's not perfect, since the "game of telephone" effect will eventually distort the original information. Still, the signal degrades very slowly, unlike with an emotional reaction to a movie, which cannot be shared to even one other person -- they have to see it for themselves.
These days the point of consuming culture is to find out information, the "who did what to whom?" stuff that a journalist would write up for newspaper readers. Is some female character really a male? Does one character betray another? Or maybe sacrifice themselves for another? This propositional information can be effortlessly conveyed from one person to another through language, and so is very easily spoiled.
This shift toward an impersonal and logical relationship with cultural works reminds me of the abstract and conceptual art of the mid-century. That was not art that you had to see for yourself; someone else could tell you the punchline and save you the trouble. I don't mean that you could content yourself with seeing a color print, or a black-and-white copy in a book, vs. seeing the original. I mean you didn't have to see it in any form at all -- "there's a series of stainless steel rectangles sticking out of the wall" or "there's an entirely black canvas" or "there's three American flags stacked on each other".
That was a sharp break with figurative and expressive art from the first several decades of the 20th century, and unlike the return to such styles during the '70s and '80s. Staring at a stainless steel cube offers the spectator no potential to leave this world for some other; it was made instead so that people, whether they saw it or not, could convey propositions about it through language. I wonder then if there was a NO SPOILERS attitude about it.
"You just have to see the new exhibit of Davidovich's work! It's so avant-garde, he's taken these stainless steel cubes and -- "
"No! Don't tell me! I'm going to the Whitney tomorrow, so don't ruin it for me!"
These shifts look like another example of our mindsets moving more in the autistic direction during falling-crime periods, and more empathetic in rising-crime times. The impersonal relaying of propositions appeals more to the systematizers, whereas the direct emotional absorption into the world and lives of others needs a more empathizing brain.
This psychological change is also linked to a behavioral change, namely cocooning during falling-crime times and being out-and-about in rising-crime times. The biggest misconception about the Romantic movement is that they were inwardly focused because of their concern with personal emotion. In reality they were more concerned with experiencing life from another person's perspective, hence their obsession with the exotic and primitive.
Emphasizing the emotional while walling yourself off from the rest of the world is pulling your mind in two different directions, since the emotional lobes of the brain are designed for social interaction. So we generally do not see culture-makers taking that stance. But where it does occur, it is always in a falling-crime period, such as the emo and goth sub-cultures of the past 20 years -- not '80s goth, whose fans got out of the house, and whose bands reached out to and found success among normal people too. Or the way too self-conscious Symbolist literature of the Victorian era, such as Baudelaire's Flowers of Evil from 1857.
It's good that they're at least trying to pull the culture away from the nerdy extreme of the people-vs-things spectrum of interests, but their hermit-like behavior cripples their ability to create works that will resonate with others. Instead it comes off as self-indulgent navel-gazing. One more reason to look forward to the end of the current period of falling crime. It won't get very high on an absolute level (at least an order of magnitude safer than Early Modern England), but the fact that it's going up will switch our minds back into the other-oriented, "people person" direction.