Does this annoy anyone else?

Well, as you said, there are plenty of people who like being surprised. So revealing crucial parts of the plot, no matter who it's to, defeats the purpose of suspense. If animê writers, or even world famous authors/movie directors revealed information just because someone approached them one on one, they would have one less surprised viewer. And that disappointment you mentioned? Authors want that. They want you to be rooting for something to happen, then completely surprise you, and for you to feel emotional, whether a good emotion or a bad one. Whether this is a good surprise or a bad one is in the has of the author. And besides, where is their evidence you won't spoil it to others? Nowadays, trustworthy people are hard to find, and they have no way to guarantee that you'll keep whatever they tell you to yourself. It isn't irritating, at least with me, it's just not wanting to spoil important things in your story, or wanting to keep it as a surprise because that's the point of the whole suspense that stories like that have.

I agree with you.

I get the purpose: the element of surprise. And it is mais realistic. As another answer points out, you wouldn't be able to find out the endgame pairing in the introduction of any book or film or TV programme.

But it is annoying. A lot of readers choose which fã fiction they read based on the pairings they ship. Someone could get halfway through a story and be really annoyed when they learn that the pairing the writer likes isn't the one they wanted. It could even be a pairing they hate.

I really hate that too. Mostly when the amor triângulo is my OTP and my hate/dislike couple in it.

Maybe they don't know themselves. There are a lot of people who make up the plot as they go, me being one of them. Just be patient, trust me, it only makes it mais interesting.

yeah totally