What we incentivize determines what stays.
I think many people just don't have a solid long-term foundational understanding of economic incentives. It's far beyond what value someone can extract today. They need to think in terms of long-term value, reputation, relationships, and how that leads to rewards. More on that here. Buying a vote may get you followers who want to follow vote buyers. Instead, consistently leaving truly valuable and informative comments on the wall of an influencer/interesting person/potential friend could lead to a life-long relationship as they engage in dialogue and follow you back. That, to me, is far more rational even from a "what's in it for me?" perspective. It goes along with making the world a better place because it's where I want to live. Add value to others because the people you want to be connected to appreciate value.
I completely agree that leaving thoughtful, valuable comments is what's going to build relationships and grow your following on here. In fact, a while back I wrote a post on my other account saying almost exactly that.
I think a majority of the unsuccessful users on Steemit aren't thinking long term. Of the successful ones, on the other hand, I think a lot more of them have a long-term view of things.