??? We're comparing the income difference (and ratio) between (poor background + college education) and (poor background + no college education) to the income difference between (non-poor background + college education) and (non-poor background + no college education).
In your example, you'd expect the Wisconsin guy to increase in tan more when you put him in the Bahamas and give him a dose of sun than the guy who started out in Miami and was given an equivalent further dose of sun.
But we've measured the opposite-- the guy in Wisconsin (poor background) does get more tan, but doesn't increase in tan (increase in income) nearly as much as the guy who started in Miami (non-poor backgrounds).
No, because we haven’t done nearly enough for the poor guy. It’s not the case that we’ve done everything possible for the poor and they still didn’t improve much. That’s false.
We're measuring the effect of one thing-- getting a poor person to college-- composed with all the other interventions that are spread through the population.
We measure the value of this-- getting to college-- as very small and even possibly negative.
We also measure interventions and their values / impacts on earnings much higher.
Going "la la la but college would be much better and itself a win if we did 50 other supportive things" is all great, but it's fundamentally handwaving in the absence of evidence.
No, we don’t measure this. The study in question tries to make college wage premium go away using questionable control variables. Sure, some skilled trades can make more money than liberal arts grads. But very few people want to be plumbers or work on an oil rig and for good reason.
In your example, you'd expect the Wisconsin guy to increase in tan more when you put him in the Bahamas and give him a dose of sun than the guy who started out in Miami and was given an equivalent further dose of sun.
But we've measured the opposite-- the guy in Wisconsin (poor background) does get more tan, but doesn't increase in tan (increase in income) nearly as much as the guy who started in Miami (non-poor backgrounds).