Large parts of the U.S., Japan and Canada all have good nuclear. Gates' has always been about pushing research in the area to get better nuclear, which he outlines clearly in this note.
Saudi Arabia for example is aiming for 15% nuclear by 2040. They have plenty of money etc, it’s just not a great solution to scale. Further, any advances you make today take a long time to put into production meaning we can’t wait for ‘better tech’.