Why does the world not care about Americans?

I have read peoples' comments on various sites that criticise Americans for not caring about other peoples' suffering around the world. If you are in that camp, then how would you account for the private donations made by US citizens to numerous charities (for the poor, medical research, etcetera)? Charity, as you may know includes international and domestic organizations; both of which receive a considerable amount of funding from US citizens who donate for no reason aside from compion. With that established, online posts made by many nationalities are calling for more tragedies to befall upon the US (terrorist attacks, natural disasters) so that Americans may be "punished" (their words, not mine) for their government's actions. The many disgusting words regarding Americans leads me to believe that the world wouldn't really give a **** if another 9/11 or Hurricane Katrina occurs. My short question is: Why must Americans be expected to empathise with those who suffer around the world while that very same world has no sympathy for Americans?