It's to prevent people from making the same thread over and over again. The Q&A thread makes sure that everything of this sort stays organized and contained. There's nothing wrong with having multiple of the same questions repeated in one thread because that's what the thread is for. But if we have like 10 threads about "How do I evolve skills with momotarou" within the next 3 pages, it gets absurdly obnoxious and people stop answering the question because it's probably been answered a million times already. Plus, the search function is there for a reason. If the question isn't in the search function, then there's nothing wrong with asking it because it hasn't been brought up yet.
you know whats really annoying? some one wont answer a question ..now THATS annoying, and no matter HOW many times someone ask's...you need to answer so do not be rude and crude about it.
If someone won't answer it for you, either test it yourself, look it up on the wiki, or find someone in game who's willing to help instead of relying on the forums for it. Making the multiple threads about the same question is probably more annoying than what you said. It's like double-posting except on an entirely different level.