What I don't understand about Bill Gates is why is he prioritising African Health Systems over his own home country's? He made his billions from corporate America and the rest of the Western World and yet he doesn't feel the imperative to pay forward to the very society that gave him so much.

This has nothing to do with with politics. It is a basic moral engagement with his own society. Of course, he can still support Africa all he wishes. But first help get your own backyard sorted.