I was thinking in terms of having the results be immediately measured and quantified. It's kind of a luxury to have such a quick feedback loop. That's all I meant by rewarding, wasn't thinking in financial terms even though that now seems like a more obvious implication.
Given the number of levers they have available to adjust in terms of tuning factors to maximize engagement, and given the changes constantly going out to their platform, and given the changing landscape of the ad market itself over time, I doubt that it's exactly clear to a developer what they're doing right and wrong. Facebook probably has a full-time staff of data scientists to extract conclusions out of that pile of analytics data.
