While the aids instill the moral hazard in resource usage, vested interest groups gain from such myopic belief. Under the rug of humanitarian action, government and taxpayers of rich countries bear the cost of giving aids but leaving some interest groups better off.
By your use of the word "must," do you mean that it is necessary for survival? If so, whose survival- the rich nations' or the world's? Or do you mean that they are bound by some other imperative requirement, such as a promise they made to their citizens found in their respective laws?
Helping the poor won't solve the problem of hunger. Even if the aid is in the form of helping countries increase their resource production (e.g. food), the central problem of ecology (i.e. excessive demand of resource) won't be solved. The central problem of hunger is overpopulation.