Who doesn't? He's independently wealthy regardless of whether startup investments got to zero or not.

Being independently wealthy is irrelevant. Do you stop caring how your investment portfolio does, just because it won't bankrupt you if it goes to 0?

Do you go to extreme efforts, enduring public lambasting simply in order to get returns on 0.002% of your portfolio? When you've already got so much money you can't give it away fast enough?

I think it takes some exceptionally motivated reasoning to believe that Mr. Gates is doing this because he only wants money.