Smaller dimensions means you can set a smaller length for the wire.

As you can see on the diagram on this article, there is a large push into increasing the height of the transistors. That has being going on for more than a decade.

About the width, a finer process means you can keep the width of the most critical transistors the same, but can also trade it off into less width (and performance) where it is less important.

So, overall, smaller dimensions leads to lower resistances. You can trade some of the gain for density, but you'll always get some lower resistance.