Princeton wasn’t taking Black students back then, and Harvard and Yale took very few. To become rich, it helps if you have a network of contacts. African-Americans graduating from Tuskeegee could have that. Those graduating from Harvard or Yale would be left hanging between two worlds, neither of which they fit into, and at least one of which didn’t accept them as equals.
To be clear, I was saying more blacks from Tuskegee became future self-made millionaires than there were white future self-made millionaires coming from Harvard, Yale, and Princeton. This was during a brief period in the early 20th century.