It's not a few billion dollars, it's hundreds, and probably decades before it pays off. Private investors have dabbled with alternative approaches to fusion that promise lower costs, but none of them have really panned out and it's pretty much all fallen to government sponsored research.

I expect private investment will pick up eventually, when the technology is a little closer to market. I'm not at all disagreeing that we should be investing more in it and that it's looking increasingly urgent, it's still a relatively small effort compared to other things.