He's not "trying to improve the world". The foundation (a) does not draw from their own wealth but rather from the proceeds of an endowment they settled on it years ago, it's a major investment fund that contributes to a lot of the problems it claims to fix by participating in the very financial processes that cause poverty in the global south, and (b) is, in reality, the method by which he influences world politics. It's very much his way or the highway. As an example, trying to eliminate diseases like malaria involves, by definition, putting resources into wholly extinguishing it in areas where it's already scarce, which is the least efficient way to actually save lives - but if you are a poor African nation either you send your money in that.very inefficient way and help Gates with his ego-driven goal of ending malaria, or you don't get access to some of the wealth that he made selling software that ran on computers whose owners could only afford them because the minerals were all-but-stolen from poor African countries.
He's also much admired for spending on education but there's been at least one instance of him saying he knows how to educate better than the experts, so this poor nation has to implement his educational plan if they want to get the money, then several years later, much money spent by the country he was helping (remember, he's not just telling them how to spend the grant, which would be bad enough, but also how they need to spend their own money if they want the grant) and millions of children "educated", the whole thing was quietly abandoned when it was discovered that no, coding a few pieces of software 40 years ago then abusing various financial regulations to amass so much wealth that you personally could end world hunger and it wouldn't affect your standard of living at all does not in fact equip you to know better than the experts how to educate a nation's children.
And sure, maybe it's better than if he kept it all. If someone only killed one person it'd be better than if they killed ten. This is not how he "helps the world". It's how he uses a small fraction of his wealth that has been set aside in an investment fund for years now (afaik he hasn't settled any further endowments on the foundation since establishing it) to exercise global influence and launder his reputation. The simple fact of one person having tens or hundreds of billions of dollars is wholly indefensible, especially in a world with looming climate disaster and widespread poverty, and doubly so when the wealth of these goons comes from the brutal extractive economic relationships that Gates and people like him have fostered with the global south and that are largely responsible for the problems he claims to be fixing.
It's all even more morally bankrupt than the already extremely shady and disturbing nature of his rise to prominence. There's a couple of rather good episodes of the citations needed podcast that is fully researched and goes into the disturbing nature of billionaire philanthropy and the way it's one big sham that both benefits the philanthropists, reinforces the systems that enrich them and extract wealth from the global south, and is a way for the ultra wealthy to exercise political control.
Episode 45: The Not-So-Benevolent Billionaire: Bill Gates and Western Media https://player.fm/1sMMSS
Episode 46: The Not-So-Benevolent Billionaire, Part II - Bill Gates in Africa https://player.fm/1sSLJe