The way the Steem blockchain works incentives everyone to be content producers.
Not everyone. You see only a part of the ecosystem and believe that this is it. There are curators, voting bots, people looking for advertisment, and many others. Soon (hopefully) this ecosystem will grow even more with SMTs.
And to honest self voting isnt even that much of an issue when compared to the other problems the Steem blockchain is currently facing.
What other issues?
I believe @kevinwong did a few very explanatory posts about it.