I'd rather say the Europeans were kept out of Africa because of nowhere near European levels of valuable resources (think farmland, wood) other than slaves for centuries. Diamonds and uranium are a recent thing.

I always heard it was a logistic issue more than anything else? Getting from Europe to the Americas and then back in a sailing vessel is easier than getting to Africa's East coast and back.

Which explains why Africa was colonized so much more successfully than (checks notes) ... Australia?