What you're alluding to is simply not true. I worked at several companies and have several friends in Atlanta area that have no such problems. I think you're extending African American population density in Atlanta to fit a narrative that simply has no backing. In fact, companies in Atlanta area are more diverse than Austin or whatever techhub you want to name, except SF Bay Area I would say.
Genuine question - how does this compare to other industries in the city? If AAs are underrepresented in tech in Atlanta, I imagine that part of this is caused by the same problems faced by AAs in other white-collar jobs. How much of it is a problem with tech specifically?
Tech firms underperform massively on this metric compared to other local industries (law, accounting, general Fortune 500s like Home Depot/Delta/UPS).
That said, tech firms in Atlanta in general have more African Americans than do similar firms in e.g. Austin or SV.
If I'm African American, Atlanta is a better place for me to get hired and promoted in tech than other tech hubs. My suspicion is that the fact that managers live in Atlanta normalizes for them the notion that African Americans can excel at white-collar work, so biases that exist everywhere are somewhat reduced here.