1) The USA tax code encourages wealthy people to create foundations. The money in the foundation is still controlled by them and has tax benefits.
2) In other countries, wealthy people are taxed to provide social services like education and healthcare. In the USA, they're not - the capital gains rate of 15% is basically a round-off error compared to 90% last century.
3) Foundations work very well for tax planning. Who knows what their efficiency is as charity?