Its a lot of things....all of the above really. I have seen single posters come in never to return....all the while several others have chimed in on the post. But, yes, when there are less people actively posting all the time, then a new person who doesn't get a reasonably quick response won't be coming back. Myself, I am very guilty about not posting long detailed responses (as I once did) to first time posters just for the reason I stated above. Once I see someone will stick around and/or is interested in hearing more from me, then I will go forth with more attention to that poster and keep returning to the post so that the person isn't lingering out there without help. I get a share of PM requests for help as well that I always respond to fairly quickly.