This isn't really an answer. There are nootropics which at least seem to make the human brain work better. The question is why new ones aren't being invented. Are the existing ones really the best possible?
And yes it's unlikely there are drugs that can magically increase IQ. But there are many other effects drugs can have other than improving IQ. Like stimulants seem to improve focus almost magically for some people.
Even the thing about evolution isn't necessarily true. Evolution is slow and random, and isn't optimizing for IQ directly, but also other things like energy usage.
So Scott Alexander's post at http://slatestarcodex.com/2016/03/01/2016-nootropics-survey-results/ shows that the most "effective" "nootropics" have still been the ones that have existed for a long time. What do these results really mean, though? Is it possible that people are just worse at noticing the subtler effects of the other drugs, or are just much worse at disciplining themselves enough to correctly use the racetams or noopept (as in, with choline)?
How much potential is there in innovation in nootropics? What is holding this innovation back, if anything? It feels like there hasn't been any real progress over the last 15 years (other than massively increased awareness), but could targeted drug discovery (along with people willing to be super-liberal with their experimentation) finally lead to some real breakthroughs?