It's not only good for the direct money (though that's nice), but also the connections to potential customers, if the source of the money is also well-connected

It's not only good for the direct money (though that's nice), but also the connections to potential customers, if the source of the money is also well-connected (not all wealthy people are well-connected too, but many are). For example, somewhat famously, Bill Gates's mother served on the board of directors of the United Way at the same time that John Opel, chairman of IBM, also served on that board, which was instrumental in getting the young Bill introduced to the right people.