In a system of equal wages you'd still get paid for developing your steam engine even if it didn't work - the safety net means that engineers won't have to take a risk (beyond wasted materials) in order to develop new designs. You'd need a central bureacracy [which is the problem] so you could apply to a group akin to the InstMechEng and they would asign finances for your project or not (or you could self-finance if the costs weren't too high).
It also however means that when they make the new design everyone can benefit rather than just them. For sure, some people will consider it only worth working to improve things for themselves and so refuse to work to make new engineering advances.
A better example you could give IMO would be something like coal miners. "No one would want to work in a coal mine, as it's high risk, if the reward is the same as working in an office as that's low risk.". I don't think it's true, some people will still want to work manually, despite the risk - people take risks for pleasure so the economics are far more complicated than "people only take risk if there's greater financial compensation".
It's a source of sadness for me that one might feel the only reason to do something is to have more than other people rather than to give more, to make everyone's world better. Greed is hard to combat, I certainly haven't managed that, but it's not the only motivation to work.