I get the question, but as is so often the case, you're ignoring the very real obstacles.
Humans are not perfectly rational. We don't have one goal. Goals rarely align very well. The things that inhibit us, with regards to reaching the kinds of goals you propose, are things that we can feel love for, need for, etc.
There is no such thing as "i could if i would". That's why mensa memberships and the like are ridiculous.
What i mean is, it is common enough to say: you are no smarter than your actions. Or something of that sort. But really you can go a lot further than that. Nobody is making decent measurements of "human potential". That's because we don't know what humans are supposed to do. No one does. Not even proponents of paleolithic diets (sorry)
An IQ measurement is an attempt at measuring human mental faculties in a meaningful way, but what if humans are really supposed to excel at abstract art over all else? What if we are actually supposed to lift heavy things? What if all lifts other than the deadlift don't matter, and you're 320 benching is completely irrelevant? There just is no sensible metric for the "human potential", that would stand up to any kind of scrutiny.
So one reason we don't all excel at benching 320 and get the best possible grades, is that there is no reason to do so.
Now... in terms of having sex with other humans, you could say that we are all in general pretty adept at making that happen. Most people end up doing it. At least biologically speaking, you can make a fair assessment that this is what we are supposed to do - but notice that put under that lens, benching 320 or scoring good grades aren't really that great at all.
When talking about sports and art, people often refer to them as by some standard "pointless". Or at least we question what is the point of them.
In my head, sports and arts is an unearthing of, or a search of, exactly this kind of thing: the human potential.
There's something about being on a basketball field and dribbling and shooting your way to an impressive scoring that just feels so right.
Likewise to behold an impressive piece of craftsmanship or art.
Even very abstract art, whether rather than in simple esthetics, the art is in the process or the thought behind it all. It somehow, more effectively than words, ends up conveying an idea in an elegant way.