Yep, that happens, but so does people extracting thousands of dollars by self-voting and voting via sock puppets on completely useless (often spam) content. Just because most people don't see it, doesn't mean it doesn't happen. It's usually done on older posts as comments to avoid being noticed. People complain about low rewards or a low STEEM price, but often they don't understand what causes those things. People extracting value from the Steem rewards pool is a big part of that. At least vengeance based downvotes can be countered with upvotes.