That's a very naive, but common, viewpoint of wealth. "Worth" 1.3 billion does not mean "has 1.3 billion lying around in liquid cash". Net worth is tied up usually in many bank accounts across multiple banks, securities, real estate, trusts, etc. And that's all excluding capital tied up in corporations/orgs. Freeing up and giving away half of a billion dollar net worth is a difficult and time consuming thing, one which requires effort to do.