Bede hit the nail on the head. What you suggest would open the floodgates to spam-mongers.
And the problem you describe is no different to any other internet forum.
The important thing to remember is that it is free to join any you can get virtually any query answered. For some people, that's enough. Not everyone feels the need to join the community once their query has been answered.
After all, I find a forum every time I have a problem with all sorts of things - but there's no way I ever intend to become a regular at all of them! You pick your favourites...
