It's a gift exchange. When you participate in a gift exchange, you are expecting a gift tailored to your interests. When you see what should be your gift handed off to someone else it's annoying.

Sorry you don't understand that, but you're pretty shitty if you do that and then expect the person who originally requested it to then fawn all over you because hey! they'll see it anyway. If they do, fine, but it's not expected and you shouldn't count on it/should understand that someone might get fucking pissed.