Trust networks are extremely valuable, and they underpin a lot of the wealth, or lack thereof, in communities.
Poorer African Americans often have limited community and cultural support systems and the implied access to trust networks.
They instead have to contend with the massive and continuous structural damage inflicted upon their communities through the history of the country, including Jim Crow, redlining, mass incarceration, social isolation, and the war on drugs.
It's amazing when you stack up the numbers from redlining, the Freedman's bank failure, these tax shenanigans, and the impact of differential sentencing for minor drug offenses propagating through to inability to access student loans and housing assistance.... (remember, if you rape someone, you can get government student loans, but if you had a baggie of marijuana, you cannot). So much money. And immigrant families, because they're coming here now, have not faced the same systematic impacts.
I'm not sure I follow. Are you saying immigrant families are in a better financial situation than the discriminated-against blacks, because they weren't discriminated against in the same way? Many immigrant families bring very little with them and have to start from scratch.
However, what they usually bring is intact community and family support structures. Trust is one of the most valuable and scarce resources there is. It can even make up for a lack of money, because valuable services are often provided reciprocally to members of the community at low or no cost, and people tolerate sharing resources more easily with people they trust.
But if there's neither trust nor money, it's a much harder struggle.
Which is pretty damning of the way America treats its own people.
Edit: I want to add that this is not simply my own speculation; this is the explanation that I've heard in part from several friends and acquaintances. They're often horrified by the leniency of standards for even high performing American students, and they will often state that they are not "black" in the way that native African Americans are, and are therefore not subject to the same biases and limitations.
A "goof off" from my community would be struggling to get Bs while a goof from the non-immigrant groups would be struggling to pass at all. And being a "straight-A student" was a baseline expectation rather than a marker of being a rare and special talent. The bar for how many sacrifices parents are willing to make to set their kids up for success is higher too. I got a B- in Math ONCE and my parents immediately hired me a tutor and started forcing me to do remedial exam drills, which is a reaction I don't think I would have seen in the average or median American household among my peer group.
I don't think it's any special level of intelligence among the immigrant community, but I think there is sort of an "Overton window" of cultural expectations for what are normal ways to spend your time, what's an appropriate spread for grades to be at, or what things you should be prioritizing in life. I think immigrant communities maintain an Overton window that prioritizes scholastics over the mainstream culture.
This is probably in large part due to selection bias since the immigration process chooses the cream of the crop, but the durability of this tendency across generations is probably set up by the higher standards I talked about.
[1] Could have come from: Can American Capitalism Survive?, Capital in the Twenty-First Century, maybe Enlightenment Now.
[2] It could very well be luck: https://arxiv.org/abs/1802.07068
Immigrating and deciding to live in another country takes a lot determination.
If you take ambitious and motivated black parents in America I am quite sure their children far outcompete the averages.