The other thing is the question of what do they think is worth doing. Imagine a person who's been enlightened. He/she may have been miserable, depressed and suicidal in the past, but now has reached state of no suffering and is completely happy. Very likely goal of such a person is to reduce unneeded suffering of others. The most straightforward way is to help others reach enlightment.
https://en.wikipedia.org/wiki/Nagarjuna
and
>Why aren't they generating awesome works of science or philosophy or literature or something with all that clear-headedness
Maybe they don’t want to? Maybe their motivation is towards intrinsic goals, while science/literature/etc. are all extrinsic.
Just because they aren’t doing X doesn’t naturally and obviously mean it is because they cannot do X. e.g. I can readily be a manager, and have more of certain (in)tangible things, but choose not to, because that line of work interests me less than other kinds of work. Just as, by the same token, just because somebody wants to do X doesn’t mean they can do it. e.g. I really want to be a talented rockstar with mad guitar skills, but I cannot becuse I am largely tone deaf.
Douglas Adams comes to mind.
“For instance, on the planet Earth, man had always assumed that he was more intelligent than dolphins because he had achieved so much—the wheel, New York, wars and so on—whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man—for precisely the same reasons.”
The individual’s? If my needs are simple, and easily met by working 2 hours a day, what reason do I have to toil 18 hour days? To enrich someone else? My skills and talents are for me to decide what to do with. What right does someone else have to dictate how much I ought to work?
All it does, really, is put people in a more focussed, balanced state of mind, and shut down much of the incessant internal monologue. Someone focussed is generally better at their job than someone distracted.
So as one of the comments mentioned about monks not producing works of art or science - if an artist/scientist really did get into meditation, and if they were innately passionate about their art/science, they would get better at it. But it is presumptous to assume that the average monk wants be do art/science.