To be clear, I'm not working from a pure philosophical game-theory perspective here--more a psychology-aware one, where we recognize that humans SUCK at gauging long-term vs. short-term benefit. If your system is set up to subtly favor long-term success but has obvious short-term potential, the short-term strategy is going to win out even if it's "irrational".
You hit the nail on the head with "the system was already set up heavily on the side of rewarding stake". Minnows exist only to feed whales; the imagery there is pretty overt! And if getting people to buy votes is an effective way to consolidate stake, even if it's not the best, just a satisfactory and easy one, that's what we'll see happen.
This outcome should be no surprise, really. Cryptocurrency in general, and Steemit especially, are capitalism in code. And the thing that capitalism does best is pillage labor to make a few people rich, sustainability be damned, even to the scale of the whole planet.
RE: @transparencybot - three points