I think there are multiple factors behind people systematically not trying hard enough:
Status / power. People who spend extraordinary amounts of work and achieve extraordinary results can be perceived as trying to get power, and can be punished to teach them their place.
Incentives are different than in our evolutionary past. Spending 100% of your energy on task A is more risky than spending 20% of your energy on tasks A, B, C, D, and E. The former is “all or nothing”, the latter is “likely partial success in some tasks”. The former is usually a bad strategy if “nothing” means that you die, and “all” will probably be taken from you unless you have the power to defend it. On the other hand, in science or startups, giving it only your 20% is almost a guaranteed failure, but 100% has a tiny chance of huge success, and hopefully you have some safety net if you fail.
The world is big, and although it contains many people with more skills and resources than you have, there are even more different things they could work on. Choose something that is not everyone’s top priority, and there is a chance the competitors you fear will not even show up. (Whatever you do, Elon Musk could probably do hundred times better, but he is already busy doing other things, so simply ignore him.) This is counter-intuitive, because in a less sophisticated society there were fewer things to do, and therefore great competition at most things you would think about. (Don’t start a company if your only idea is: “Facebook, but owned by me”.)
Even freedom and self-ownership seem new from the evolutionary perspective. If you are a slave, and show the ability to work hard and achieve great things, your master will try to squeeze more out of you. “From each according to his ability, to each according to his needs” also makes it strategically important to hide your abilities. Whether harder work—even when it brings fruit—will lead to greater rewards, is far from obvious. Even in capitalism, the person who succeeds to invent something is not necessarily the one who will profit from it.
This feels a bit repetitive, and could be reduced to two things:
1) Whether the situation is such that spending 100% of energy on one task will on average create more utility than splitting the energy among multiple tasks. Assume you choose a task that is important (has a chance to generate lots of utility), but not in everyone’s focus.
2) The hard work is going to be all yours, but how much of the created utility will you capture? Will it at least pay for your work better than doing the default thing?
To use an example from Inadequate Equilibria, even if we assume that Eliezer’s story about solving the problem with seasonal depression is a correct and complete description of the situation, I would still assume that someone else will get the scientific credit for solving the problem, and if it becomes a standard solution, someone else will make money out of it. Which would explain why most people were not trying so hard to solve this problem—there was nothing in it for them. Eliezer had the right skills to solve the problem, and the personal reward made it worth for him; but for most people this is not the case.