They're dumb because they're poor <-> They're poor because they're dumb.
Setting aside my moral issues with the idea of Economic Phrenology I think this is an acceptable checkpoint to stop at when trying to reason out an answer. Feel free to stop, look around stretch out your legs. And then get back on that train of thought and take it to the end. Why are they poor?
There's the circular logic argument of "well cuz they're dumb" but that ignores generational wealth, the gender wage gap, systemic inequality, luck, economics, and just a general lack of equity of opportunity.
Some people smart people choose low paying jobs because it brings them a fulfillment money cant. Some dumb people get rich off the lottery.
And like... We've all seen rich peoples kids. They're not all geniuses.
It's just not a coherent belief. It is demonstrably not true.
"Dumb" is just a projection. It takes a lot of checked boxes to become successful. Yes, one of them just may be a hereditary propensity to value reward more. It's not an incoherent belief any more than that some people could never play in NBA, it just takes another set of boxes, some of them hereditary.
I remember high school, coach organized a wrestling match played out over a week. You had 32 matches. The winners competed in 16 matches. The winners of that competed in 8 matches. Then 4 matches, then 2 matches then the final match.
When you've built an economic system that distributes wealth that way you can't cast moral aspersions on the losers. Because that's what it does, creates losers by design.
There's repechage, and there's plenty of repechage in life.
At the same time, yes life is not fair, and that's not really a property of the economic system anyone built.
Why?