The lack of advertising is huge for me. I developed the habit of avoiding products that I recognize from advertisements - because if all that money had to go into promotion, it certainly didn't go into creating a more valuable product for me.
In many ways, Steemit is a return to the gift economy of more traditional societies, and I think this appeals to people in a big way too. Especially as jobs disappear and meaningless labor becomes a thing of the past, people are eager to find ways to give and contribute. Steem allows them to do this both through their time and creativity and their investment.