Because that is what people actually want to see. And it works better here because users reward it. Instead of just being a number clicking on something we are now more powerful with our voting ability. It means so much more on Steemit. Because it has higher value inside it.
Main reason why it works is because there is so much higher value being created and rewards given out. In a way we have always been able to do this but it's been more complicated to exchange value. Now it's super easy and we can give proper rewards for content. And the sum doesn't really matter that much it's more that people feel that they are finally being appreciated by someone.