While you have a point about social policy within our own countries, can we rely on our governments to have a policy for overseas disasters? Indeed would our electorates even want this?
After the tsunami charity was able to collect donations and target it into affected areas relatively quickly while governments made initially small pledges and then tries to outdo each other as the scale of the private donations was revealed. Pledges from governments as with all relief were slow in actually being realised if they were at all.
Governmental aid of all types is also so often tied to ridiculous and inefficient conditions such as insisting on donor country companies being used when they cost magnitudes more than local companies.
If we want to direct money abroad for any relief, health, social reasons we have little choice other than to do it through charity.