It is a free market economy. Since content is not a limited resource, my consumption or my likes do not restrict others from liking it. However, upvotes, do give your content more visibility, compared to other content that is not upvoted as much. And the reward you get $300+ is a limited resource, there is only a limited amount of money and steem going around. So... Content itself may be a common good, but upvotes, steem dollars etc are a total free market. And totally scarce, limited goods.
Welcome to agora! :D