Why hasn't Elon Musk invested in controlled nuclear fusion reasearch?

I was just curious if anyone had any idea why the world's richest man, Elon Musk, hasn't invested in controlled nuclear fusion research? He hasn't at all, not a dime, as far as I'm aware anyway. This, despite the fact that he has a degree in physics, and even was briefly enrolled in a graduate program in physics at prestigious Stanford University. He even says physics is still, and has always been, his greatest interest. So, why are fellow super-billionaires Bill Gates and Jeff Bezos increasingly heavily invested in controlled nuclear fusion reasearch, but, "physicist" multi-billionaire Elon Musk, not at all? This seems kind of strange, to me, anyway. Any thoughts?