Sorry but spending / donating money is not a difficult thing to do. If you have billions of dollars, claim to be donating much of it, but somehow your wealth continues to increase, perhaps you’re not trying hard enough?
There's no "claim" - those donations and the records of the foundations are a matter of public record.
Also, completely liquidating and giving away his assets would result in a large payout once.. and then nothing ever again. You need money to make money, so holding onto some to appreciate in value (investments, interest, etc) results in more money being donated over a longer amount of time.
