Normally I'd avoid doing the feeding -- but what the hey - it's a Monday.
You'd like a satisfactory explanation -- okay. Fair enough. From 1791 to 1965, the statement "The Man is keeping me down" was actually true. It was the law of the land for things like "Separate but Equal", "No You Can't Ride Here", "No You Can't Have This Job" - etc. Second Class citizenship and all the trappings that go with it. Those that were successful in spite of things (Arthur Ashe, Bill Cosby, Diana Ross) were the exception to the rule. Since 1965, the official government rules were changed but things didn't change in the job market for another decade or so. Look up Red Lining. It is hard to get a house somewhere else if you can't get a loan for it, or if you do get a loan, the interest rate is so far above and beyond what the market rate is... And there are still places where the color of your skin will determine a multitude of thing.
Now we all know that networking helps to provide opportunity, and a lot of networking is done during the college years. If you can't get into the colleges to network in the first place it is hard to get the networking...
In any event, to match the comparison between the Vietnamese immigrants and Black Americans - the Black Americans are about a generation behind - the kids that are coming up now are being exposed to the same opportunities and are starting to be able to prosper. There is a lot of institutional backlog that is only now going away. Give it about another 3 or 4 generations.