As a server who worked every floor imaginable for 20 years I can say with certainty that Black people are the worst tippers period. I don't know why but they are.
We are talking 5% or less as a rule. Next worst were Chinese at pretty much 10% across the board but they are very easy to take care of, in and out quickly to turn the table as well.
Black people would be slow, difficult, demanding, condescending on top of it. Fortunately they are also too cheap to dine out much so tables of them were rare. And my hostesses liked me so they would steer them to other sections when possible.
Best tables ever were American business guys. One table of four could make my night.
And that's just an observation. I still served them to the best of my ability because occasionally they would surprise me(and I take pride in my work).
It is what it is. Could be cultural. Australians were the same. I would put it down to ignorance but if you are traveling regularly then you should pick up and defer to local customs.
For sure it's some of it a cultural thing. If your taught as a young person you whole life not to tip for reason XYZ, and all your family relatives don't do it, for sure mind set will be skewed to think there's nothing wrong with it.