Eh, I would say he puts a lot of effort intro creating image of benevolent nerd philantropist. Point in case: https://www.youtube.com/watch?v=0hnZJIRd6Qw There must have been a team of people dedicated to carefully crafting this video, creating props, there's even a dozen or so actors there (each in the background for just a few seconds). It looks like someone put a lot of effort into this and it surely consumed thousands of dollars (my uneducated guess is somewhere in 10-100k$ range). To what end other than working on his personal brand?

Speaking of malaria, after googling for 3 minutes it seems he spent around 2B$ on it. Does it really matter? Yes and no. Maybe it had impact on people's lives, but given Gates' net value is 100B$+, giving away a billion or two does not matter. It will not affect his quality of life in any significant way. He could give away a few dozen billions more and still will spend rest of his life living in luxury that I could only dream off. Sure, better to fight malaria than buy another yacht, but still, it's easy decision to make when you have that much money.