Oh, no! The ultimate gotcha question. There's no way I can answer "if systemic racism is real, what about black mayors?", it's impossible!
Oh, wait. I can answer.
Just because you won an election doesn't mean that all the people staffing and enabling that system instantly and wllfully change their behavior. It's hard to get a group of people to change doing 1 thing like coversheets for TPS reports, let alone "how it's done."
Also, here's a great article by the Atlantic on this exact subject.
https://www.theatlantic.com/magazine/archive/2020/10/black-mayors-southern-cities/615469/