I wondered that myself when I first was going over the structure. Anyway they do have some interesting takes on the upvoting of oneself, they actually applied the term called N-Person Prisoner's Dilemma to it. (page 14) Also that the platform is characterized upon what they call Zipf's law (page 16) and basically has the same psychological effect of that of a gambler.

https://steem.io/SteemWhitePaper.pdf

...don't forge to read the crab bucket story