First, in my opinion, spoilers gets more attention thus let others go after the information they needed to know. Then once they read it, it helps clam their conscious for the answer they seek for their question. In another phrase, it's better to see it and believe it. Thus, these spoilers are not ruining the reader's fun, but makes them have closure. It's like a person cheating a test or homework by copying someone else's paper to have the correct answers. In the end, spoilers are the best exploits to get more readers and criticism. Plus, you don't read the spoilers since you don't like it. In the end, be happy that at least the people post up a warning sign of spoilers so read their comment.
Why do people feel the need to write spoilers in topics? Like ok we get it you read new chapters, you don't have to write spoilers in topics.