It takes no time or effort whatsoever to form an opinion about post like this. So people can vote on it immediately. Whereas actual news is more often complex - and might take some time to read and process before the reader understands what it is about. They aren't going to upvote it if they don't know what it is about. And even then, there is a tendency to only vote things that trigger some kind of emotional response. Post that neutrally inform the reader generally don't make people think "yes! Lets get more people to see this."