It's because it doesn't hit home. Africans are not a worry in our minds. Our country is. If it becomes something that can affect us, too, we will care. Example: AIDS. If it is too far in the past, we lose sympathy for it. Example: Every war over 300 years ago.
That is how humans think. You cannot expect someone completely unrelated to something else and with no contact to that being to feel empathy. The species would quickly die out that way.
In addition, those who get butthurt about religion and 9/11 are not those who post these. You are generalizing a species too much.