You are forgetting about access to loans, investors, and resources to start up a business. Back in the 50s, there used to be many Black businesses, but with the change in the economy changing in the years passing, as well as urban flight, Black businesses lost money and potential investment. At least that's my understanding of it. Also, many Asians or Middle Easterners who come into neighborhoods may lower prices and costs, deterring Blacks from starting businesses that could be competition.
I agree that there needs to be a vast number of different businesses. There's nothing wrong with people selling t-shirts or music if they are looking to break into fashion or music industry, and need to make money. I don't understand why people think that's terrible, if that's legitimate, and what a person wants to do.
T/S, I encourage you to start your own business, if you don't see anyone else doing it. People naturally follow suit.
But then again, I don't believe in capitalism by any means, so I could care less about people being millionaires and just opening businesses for the betterment of their community.