He'll donate to a trust/non-profit he controls that will direct the investment. That allows him to take the tax benefit today and keep the money
It’s not like he needs these funds to buy groceries or pay the mortgage. He’s essentially hoarding assets like all billionaires are.
This is a simplistic example for illustration, the actual financial engineering would certainly create much more complexity in order to obscure things for auditors and the like. But the point is that he/his fiduciary is the one controlling it all.