It is an incredibly fair question, and part (not all for sure) but part of the reason is the United States offered, both because it’s a traditionally liberal Democracy, but also because it’s wanted to project the soft power, that comes with donating Billions in aid to nation which it hope will look upon the US favorably when it come to Trade & Security negotiations. It’s serves the US to project and maintain this soft power, and it assists Tyrants and Democratically elected governments all across the world assist their own citizens, for “free”. Some nations have become so dependent on the “free” USAID it’s not even an afterthought in it’s own budgetary process, and for most of the USAID recipients they simply cannot make up the financial shortfall to fund these programs on a dime, most couldn’t ever pay for these programs out of their own budgets ever. Some countries take advantage of the US, countries who can easily pay for the same services that USAID funding provides, but would choose not to because when put to the choice, they’d choose to let their people suffer.