We feel like helping others in these situations is simply the right thing to do, and our governments are better able to do it than individual citizens.
I would argue that the government is not better able to provide charity than individual citizens. For example, the Zika funding bill was voted down, because members of congress disagreed with each other. If Zika funding was provided through voluntary means, then we would not have these stalemates and delays. I won't say that private charities are perfect, but at least you can choose the private charity that you want to donate to; when it comes to government, you only get a "choice" every couple of years, and it's usually not much of a choice.