How does this imply that the cause is racism?
It implies a
difference that is explained by race. That's all. It simply says that, of the variables we have access to;
race accounts for the majority of the difference between the distributions.
By definition, that means "race is the explanatory variable". How that manifests is a different question.
What if we took a statistic on which race had the most spinners installed on their vehicles? If Asians or whites had a lower number than blacks could we conclude that it is the result of racism?
You could, then, conclude there is a difference explained by race.
Of course not we would conclude it is the result of preference or desire.
But if, on average, black populations have a preference for spinners at a higher rate than white or asian populations then indeed it appears to be a racial distinction. You can, of course, dig in and figure out if it is more likely something deeper (is it a COMMUNITY preference?). But right now we KNOW that we can explain income differences solely based on skin color.
The point here is simply to establish if there is SOMETHING THAT WE NEED TO LOOK INTO. Which, clearly, there IS. What is that? Well that's where we do have to look deeper.
So, again, what accounts for the
systemic difference between incomes for black and white Americans?
When you figure out that the problem EXISTS then you can start to ask the MEANINGFUL QUESTIONS.
What's your guess? We have already established that there IS a difference, now what do you think is that difference?