I see it as different markets, FB is about connecting with people you know and the people they know. G+ is all about finding people you don't know but who share some of your interests. Steemit is a little bit of that, but more geared to blogging than resource sharing. The gamification has meant that for me, at least, I switched 90% of my time over here, feeling like I'm neglecting my friends in G+. Lately all I post over there is links to here. But I have nearly 5000 followers there, and with affiliated links, I could reach several times that number.