The problem is that corruption is widespread throughout most of the world, and especially places in poverty. A stable, just society is able to bootstrap into relative wealthy pretty quickly, so most of the countries that have the largest need of aid, also tend to have the greatest issues with government trustworthiness.

As an aside, some charities are scams, but many are not. There are tools you can use to determine which ones are trustworthy, but some basic common sense goes a long way too.