Good content improves the visibility of Steem(it) in Google and other search engines and could bring more traffic and potentially more users. If users see that good content gets a lot of upvotes, they are more likely to produce good content for our system. Also they are more likely to tell their friends about Steem. I don't know if that's the key alone because there may be other keys to success like games on Steem or a combination of many things.