If high IQ jobs offered in-building day care as a perk this trend would completely reverse.
Convert the parking garage in the basement into a day care and you'll have phd-level employees for life. Changing jobs for even double the pay would be completely unaffordable.
The negative correlation between education and family size is a function of the cost of raising children in a city. If the cost is reduced then the correlation becomes nuetral or even positive. There is no such correlation in a rural setting. This is a bottleneck in the talent pipeline.
Consider this paper (from Indonesia) in which concluded that the relationship can change over time, as a function of policy: