I don't know what your options were, but here are some reasons for the US to provide support to countries in Africa:
-moral reason: it's morally right to share the wealth
-humanitarian reasons: we care about other people and we don't want other people to suffer
-economic reasons: if the US provides aid to those countries, it can later invest in them too, which will be economically profitable.
-it's also generally good if other countries are also rich, as they can be a potential market for the US goods