Because sadly the world doesnt work that way. Imagibe if you had a black peter parker in segregation era. Could Peter be black and still go through the exact same things? And i am not saying that because being black inherently different. Its just that black people go through different hardships due to inherent racism in america. It is not racist to say people with different backgrounds have different cultures and values.

And there are cases where this is not important, for example in the new batman film we had a black Jim Gordon and it was great. But again that is just my opinion.