One of the reasons that private charity is somewhat looked down upon in certain countries with a robust welfare state is that historically, private charities were selective in whom they helped. If the private charity felt that your "lifestyle" (i.e. you were a mother out of wedlock, you were LGBT) or ethnicity was objectionable, you were just left to suffer. Or those private charities would assist you, but you were obliged to convert to their religious denomination or sit through a long sermon before getting to eat.

Welfare states run from taxpayer money and overseen by democratically elected officials, while they have their downsides that are often commented on, at least tend to assist groups that would be marginalized otherwise, and there are no religious strings attached.

Because thats where the money originally came from.

Why should the single billionaire get to chose?