I disagree. The "WHY" is critically important in making policy decisions.
Currently, the accepted wisdom is that statistical group differences in performance is entirely due to environment, and that by sufficiently improving the environment of the lower-performing group, the group differences can be eliminated. The perceived duty is then to spend as much as needed to eliminate the differences.
If statistical differences in average group performance has a primarily genetic basis, then NO amount of spending will erase the difference.
This is why there is such hysterical upset whenever genetics is mentioned -- too many people would lose money and power if we stopped spending money on something that will not get fixed.
Head start programs and busing are cases in point. Liberals insisted that by dumping more money into various social programs and by moving inner city black kids into schools with middle class white kids, their academic performance would improve. It didn't. All it did was spend a lot of money and resources that could be better spent elsewhere, all the while creating problems for those kids who were actually learning.
Indeed!
But; since the 'WHY' has NOT been defined (to everyone's liking) then it is all a useless exercise; being engaged in for, as you've pointed out, "making policy decisions".