Charities can't just magucally scale up, and you NEED to verify that the money is spent properly. Even UN aid only manages to hit something like, what, 80% of the money actually being used to help the recipients while the other 20% goes go verifying the funds were spent properly and paying people to facilitate the aid, i.e. labor, gas and other forms of overhead.

If yoy just donate 1Bil to a homeless center, wtf are they gonna do with that, exactly? They only need enough to build some affordable housing to house the existing homeless population, so do they build a bigger housing complex and attract morr homeless people to the city, or do they branch out to other cities and trust other groups with the funds and hope things go smoothly.. etc.

The right amounts to the right people matters, and always use a trust instead of a lump sum. People will take the sum and run, but they'll keep at it for that drip feed of cash from a trust.