He mostly used it for two things. One, as all rich people do, to donate money to their own foundations to save taxes. Second, to push his thoughts and interest on what should be research and what shouldn't.

He didn't do either of these things overtly (e.g. as Musk for the latter), but still Billionaires do Billionaire stuff.

Probs also might have helped his image with Billionaire friends and the public.

There are plenty of times when his funding things interfered. Alas there are for sure times when his funding things helped, but no one individual should posses such power.

Bill Gates wanted to think of himself as a good person. Charity was his attempt to prove himself as a good person, and Effective Altruism got so much funding and PR because it tries to make billionaires look like good people. Effective Altruism argues that rather than looking at someone's actions, you look at how much better they are than what would replace them if they didn't do that, and then argues that there will always be more billionaires that are exploitative because that's how the market works, so that doesn't count, while not every billionaire makes a charity, so that does count.

The problem for EA is that many of the charities it recommends have to engage in lobbying to be practical, but if you allow for lobbying then obviously lobbying for legislation that reduces billionaire exploitation would be beneficial, and that's not what their donors want. So EA had to drive itself insane to curve away from that obvious conclusion, with people that still insist on it being pressured out of the movement.

But the result of that is that the ethical philosophy that billionaires wanted to rely on for indulgences for their sins had now become obviously insane, even to most of them. That's how you get people like Peter Thiel not giving a straight answer to whether humanity should survive, that's how you get shrimp welfare, etc. etc.

Gates doesn't like the insanity, but that that leaves him without moral excuses. So with other billionaires throwing their lot in with Trump, he does the same so he can at least stay rich for longer.