The "Wall Observer" is a great example , I do post there once a while, it's nearly impossible to find 3 consecutive quality posts there, and every time you hit F5 you see new post/s coming in,also notice that signature is disabled there, so nobody does get paid for posting there - it makes me think that people don't shitpost just to get paid, they either do it for fun or simply do it because it's all they know !
I think a lot of these posters just try to get their Activity up and just wait and see how much Merit they can get afterwards.
As for necrobumping, I have no problem with that, as long as the bumping post is relevant and on-topic. I prefer necroposting to opening another thread for a subject that has been discussed in the past already. Keeps everything neatly arranged and makes it a lot easier for people searching for info, if they don't have to read into 17 different threads about the same subject.