Because it is mostly a site for press release type content, I suspect Product Hunt has less incentive to discourage those sorts of get out the vote activities versus Hacker News. And Hacker News users have more incentive to flag posts that rise for reasons other than interesting content or comments. I mean, if I have an informed expectation of what I will get on the Product Hunt front page and it is different than my expectation about the HN front page in part due to the way get out the vote activities are treated.