Donations are volentary; selective; on the whole, less than the amount that would have been gained through taxation; and tax deductible.
Often, by donating a small amount, rich people can save a much bigger amount from tax deductibiles.
In addition, most of the donations goes to the rich’s pet charities, some of which use that money for questionable if not downright harmful activities, and even the ones aiming to do honest good are often run by family members or friends of the rich donors, who usually have zero experience never mind expertise in running charities. So not only do you get less resources from donations than from tax, that resource is very inefficiently used in many cases.
There are good reasons why key public services are funded through taxation and not voluntary donations.
Ok but USA had its philanthropists Andrew Carneige of the 19th century and probably rated as one of the worlds richest men anhe believed in using his fortune for others and doing more than making money. He wrote....
"I propose to take an income no greater than $50,000 per annum! Beyond this I need ever earn, make no effort to increase my fortune, but spend the surplus each year for benevolent purposes!" (source wiki)
and in the 21st century we have Bill Gates. and there's probably hundreds of like minded folks in between them.
It would be nice to witness a Chinese gazillionaire have a similar mindset.
Meanwhile In NZ we had a businessman, sick of government dithering make an offer which was accepted to build and donate a new Hospital ext at a personal cost of 50-60 million dollars.
Now thats a lot of after tax money he is offering to give away. During the same period the govt which had difilculty in allocating money for the ext/build wasted 40 odd million dollars on a referendum about changing our national flag.