really, we should help them for reasons of empathy and morality (helping those with fewer resources).

but in terms of diplomacy, our allies trust us less when they see us hoarding our wealth rather than using it to help others.

if you really want to think in mercenary terms: improving the health and wellbeing of other countries improves foreign markets that American corporations can sell to, and distributing aid gives us an opportunity to engage with nations and make personal connections to advance our national interests.

but really, we should help them for reasons of empathy and morality.