You are making an assumption that if you have 30 kids in a class who are paying and you add 1 non-payer it doesnt cost anything more to educate them. Unfortuantly thats not true, It does cost more to educate the non-payer.
In a perfect world all Kids should get the proper education, but the world is not perfect .
There are organizations that raise money for tuition, Kars-4-Kids / Oorah, but how much do you really think that raises and thats likely the biggest one. it probably raises a few million, but the shortfall is much much greater than that.
And most Gviers who give big money expect bigger control over the money. They just dont write a check for $5 Million dollars without conditions. They want to make sure they money is well spent