Often the "Why would you want to do that?" responses are because the responder believes, rightly or wrongly, that the questioner is considering something that is in some way stupid or even dangerous.
Other replies not directly answering the question are often because the asker seems to be looking at things a bit myoptically and missing a possibly better, more general solution to their dillema.
Sometimes it's just the nature of this being a discussion forum, and people discussing stuff. In that regard it's not much different than the water cooler or breakroom table at the office, where if you ask about the best hammer for framing a shed you may end up learning more than you wanted to about pneumatic nailers but have no better idea of what style of hammer to try.