So in a society where intelligence was not valued - yes there would be less environmental pressure favoring greater intelligence.
But in general and in most human societies - intelligence is valued and intelligent people are favored by sexual selection - as well as general run of the mill selection - intelligence also contributing to affluence - which is also highly favored by sexual selection.
And there need not be a “dramatic increase” in reproductive success for a favored gene to reach penetrance in a population - just a minor incremental difference over many generations.
I believe there is measurable mate-selection preference between the profoundly stupid and the moderately intelligent, but in regards to mate-selection I believe that the average male is intelligent 'enough.' Additionally, it's only been fairly recent (in terms of human history) that hyper-intelligence has translated to much greater wealth than the moderately intelligent. A moderately intelligent hunter/gatherer could produce as much food and acquire as much wealth as a hyper intelligent hunter/gatherer. Neither the (hypothetical) hyper-intelligent hunter/gatherer nor his off spring gained any reproductive edge from the increase in intelligence.
I guess what I'm trying to say is that there haven't been enough generations of humans, during which hyper-intelligence would make a reproductive difference, for selection to occur and make an impact on the gene pool. The fact is that the opportunity for this type of selection to occur is passed: we pay the least capable among us to reproduce, which in turn causes the capable to have fewer children due to the lack of resources (taxes for socialism). Sure, it's possible that we may witness an increase in the number of geniuses but they'll be swamped by the moderate and low intelligent.