I'll do my best to be concise and not write a book here.
The entire Socio-Economic-Political spectrum of the country was not favorable to Blacks. Blacks were considered actual property and completely devoid of all rights. Thousands of laws directly and indirectly reinforced it. This led to a socio-economic climate that likewise was not favorable to Blacks.
If you look the GDP as a pie chart, how much of that pie charts did Blacks occupy back in 1865, 1885, 1905...?
If you were to categorize jobs by positions of authority and power, what percent of those jobs were owned by Blacks in 1865, 1885, 1905...?
Now, think about living everyday life and getting "ahead" in the rat race. How did Black schools in 1905, 1925, 1945... compare to White Schools?
How did the law treat Blacks as compared to Whites in 1925, 1945, 1965???
What is the lag between changing a law and society embracing a new philosophy driven by said new law?
It is easy to look at an exceptional person like General Colin Powell and say, "Hey, see here is a Black person who had the deck stacked against him and he did great, why can't all Black people just do that?" Well, you can't look at someone in the top 1% of their peer group then make the argument that the entire peer group should be just as exceptional as the top 1%-er. That is not how math works.
Then there is police treatment and targeting of Blacks, the War on Drugs that completely obliterated the Black Community and led to a host of socio-economic-political problems that we are barely starting to reverse today.
In a nutshell, it takes time for laws to change and impact society on a large scale. I am not talking about one or two cherry picked exceptional people, I'm talking about an entire class and population of people. A people for whom the actual written law was against them for the majority of the 20th century. How quickly do you think a society changes?
Normally, I would never try to engage in this sort of argument online. but to your credit, you seem fairly open to debate and considering the arguments of others. This is a complex argument though and to do it justice I'd need a 100 more pages. But again, in a nutshell, it is simply a matter of cascading cause and effect.
The children of college graduates are far more likely to do better in school then the children of parents who never went to school.
The children of CEOs and Executives are far more likely to do better career wise then the children of parents working minimum wage.
The children of criminals are far more likely to engage in criminal behavior than the children of law abiding tax paying citizens.
So, simply apply the above to history.
How much opportunity was their for blacks to obtain education back in 1885? 1905? 1925...?
How much opportunity was their for blacks to own their own companies back in 1885, 1905, 1925...?
What does the above mean for the likelihood of success for their children.
Rinse and repeat the above for 1945, 1965, 1985?
Apply the results to the entire GDP of America as well as various jobs and positions of authority.
I will wholeheartedly agree that things for Blacks in this country are getting better. It is much better being Black in 2018 than it was being Black in 1968. But the people of 1968 that were racist and the policies of 1965 that were racist can still be felt today. The son of some CEO born in 1965 would be in their 50s now and likely running his Daddy's company. What are the odds that company is going to be open and accepting of Blacks?
now, I'm not arguing that every company is racist nor is everyone from the 1960s racist. I'm just arguing statistics and likelihood of influence of the socio-political-economic factors would on large segments of the population.
It is cause and effect in a string of cause and effect that dates back to Slavery. With time, things get better, the influence wanes. One day, it will be insignificant but that day is not today.