The Microsoft years proved that he was good at making money using dominate-a-market monopolist techniques.
That's exactly the wrong personality profile for someone trying to do effective philanthropy, which requires unusual empathy and cultural sensitivity, as well as tactical cleverness.
Gates - arguably - demonstrated the latter, albeit only in a very specific and (IMO) self-serving way. He also made plenty of spectacular strategic errors at Microsoft which harmed MS customers, MS competitors, and computer users in general.
So his record of strategic foresight is patchy at best. And there is no evidence at all that he has any unusual talent for empathy or cultural awareness.