I believe it's because some of us are tired of seeing people post a question, get an answer and never come back to contribute.

Many of the forums here have FAQ sections, and it looks to me that people generally do not read them carefully enough. After I signed up for FT, I spent a couple of weeks reading through the boards (mainly MP board which I'm most interested in), and then started posting. I believe faults are at both sides. As FT gets mature, regulars here see the same question over and over again and lose patience while newbies here do not read through the posts enough yet want instant answers.

And I'm guilty of posting something like "Use search function" once or twice