It's not width, it's depth. Things like gate oxide are deposited as a layer through a chemical process. That layer is the same thickness across the entire chip,

It's not width, it's depth. Things like gate oxide are deposited as a layer through a chemical process. That layer is the same thickness across the entire chip, and it scales down with the node. Gate oxide thickness determines your maximum gate voltage. Chips aren't 2D structures, they're built out of 3D layers and all those layers have a constant thickness.