You expect everyone to be perfect which cannot happen.
And related to thread, if someone has joined this thread today then it is obvious that he may not be able to find the previous threads as well.
The quality of a response is pretty highly positively correlated to the quality of the request. I don't expect people to be perfect, I'm just describing those things that increase request quality.
"Being able to demonstrate being able to locate existing information" isn't a prerequisite for receiving a response, but I also don't feel bad when I don't respond because of the lack, or when my response is to point people to that already existing information.