Some of the charity is self-serving, e.g. eradicating diseases means he's less likely to catch them (and really any billionaire not funnelling funds to pandemic prevention etc. is being moronic), and founding charter schools on land he owns so over the life of the school they pay more in rent for the lease than they cost to build is just a tax dodge. Most billionaires are just so evil that they won't spend money on themselves if other people who aren't paying also benefit, so in comparison, Gates' better ability to judge what's in his interests makes him look good.