That's because Bill Gates listened to the scientists, and you can see him write about this. He knows to not put all his eggs in one basket. So he invests in small nuclear, because it is a technology we have and can fix deployment issues. He invests in solar because it is a far cheaper option in sunny areas. He invests in carbon capture and sequestration to reverse the effects of climate change to this point and how we'll likely continue to pollute. He invests in battery technology so we can use those renewables without a base load (really would be a phase in). And he's investing in fusion because it could make all these questions obsolete. He's investing from many different angles because you can't really predict what will work.

There's this weird myth of "either or" here. People are treating money, labor, and materials as if they are these static things. This isn't a video game where if you need more pylons you just buy them. In reality we only have so many experts in a field at a time. We can't just solve fusion faster by throwing more money at it. There are diminishing returns after a point. So you use this money elsewhere. This weird myth of "either or" really comes down to thinking that everyone is stupid and "I'm an expert" (the "It's so simple, you just..."). I find this odd on a site full of tech nerds who have to frequently deal with these types of logistical issues and laymen making wildly naive conjectures.