How come it seems nobody really cared about spoilers as much before the 2010s?

[1924]

It’s clear though that back then nobody really cared about spoilers as much for whatever reason. Movie trailers basically summarized the whole movie in 3 minutes. Novelizations for blockbusters would hit stores a month or more before the movie came out. Critics like Siskel and Ebert would show off plenty of spoilerific clips with permission from the studio. On the Youtube comments for The Two Towers trailer you can see a lot of comments from likely younger people amazed that they “gave away” that Gandalf returns Or that the T2 trailer “gave away” Arnold being the good guy this time even though to the studio l, that would seem like the obvious selling point of the movie