Despite what some of our societies’ most dogmatic cynics believe, most people actually do wish to make contributions, learn about the world and each other, and help everyone satisfy their basic human desires and needs. Carrots and sticks don’t turn apathetic people into productive contributers, they just turn well-meaning humans into recalcitrant mules.
We've fallen into a false premise that ROI can be applied to everything. We don't even know how to determine ROI for education. We have ideas about it, and every few years we have new ideas about it, but rather than trying to hard to maximize ROI, we'd be better off just killing it by investing in those fundamentals. It's like raising a kid. A good parent doesn't give a damn about efficiency when trying to raise their kid. You just flood them with good examples, and opportunities to learn. Make people fight over teaching jobs, and give the kids more attention.
As for bonuses, IMO they most effective when the job sucks and/or doesn't pay enough.