My nuclear power plant shares its site with a coal plant. The coal unit produces a quarter of the electricity my nuclear plant does. The coal pile currently contains enough coal to operate for 3 days. My nuclear plant has enough fuel inside the reactor to operate for 4.5 years. My nuclear plant has been operating since 1971, and all the fuel we’ve ever burned (and still store on site) is many times smaller than just that 3 day coal pile.
Where else are you going to get energy densities like that?
1 uranium fuel pellet is the size of a pencil eraser.
E = mc2, baby.