Translated the comment.

What makes those Steemians upvote your posts?

1. A successful SNS' market capitalisation is huge. How Steem works is, the market cap is distributed to Steem holders. It motivates Steemians to upvote quality posts. By metcalfe's law, the more number of users, at some point the value of Steem Network will grow exponentially. We're expecting that.

2. Most people have desire to enact their own justice. What postings deserve how much rewards... So they Steem Power Up, upvote or downvote.

3. Curation Rewards... To discover good postings early thus to let Steem Power Whales follow up after my upvote will give you back some incentive in return. It's not much, but it's still some rewards.

Selfish individuals' activities can be the energy to grow this platform.