Hadn't considered that, but you're correct. It's not like he needs publicity.
At any rate, even if he was simply tired of not seeing his name in the media enough, and thought this would be a sufficiently grand gesture...I don't mind at all, as long as he's being even moderately effective with his money.
Mark Zuckerberg annouced that he is going to give away 99% of his facebook wealth ($45 billion) over his lifetime.
He announced guiding questions:
It's interesting that "live much longer and healthier lives" is on the list. Larry Page seems to divert money inside Google into Calico for anti-aging tech. Under Cook Apple also invests into health.
The future seems looking good :)