You have your spammers that want to get their posts and the down votes give you a clue the item or advice is not that good.
The moderators do their best to eject the spam but if they are crafty the post stays but at least we can vote it down.
Back in the middle days of discussion forums this thing called 'voting' was introduced. It was alright for a while -- you could vote a post up if it was good, or vote a post down if it was rubbish.
Since then the system has been abused, much like "YouTubers" abusing the right to uncensored comments.
In response to this, board admins decided to remove the down vote button from their boards.
The rationale was that abuse would cease, forcing people who didn't like particular posts or replies to either a.) ignore the reply or b.) comment on the reply.
Isn't that what forums are all about?
Proponents of the down vote button like to argue that the down voted posts are more easily 'ignored' or forgotten. How is that so?
I maintain that down voting is a form of personal attack, albeit one that allows a loophole in the whole "do not post personal attacks" rule.
I believe that if one finds a post useful enough, it _will_ be voted up. If one finds a post truly offensive, then that's what the 'report abuse' button is for.
If one simply doesn't like a post, they can move onto the next.