Smaller process means less energy. Less energy means less heat. Less heat can mean faster operation. So without changing any of the layout or logic of the chip itself to make it more efficient, just shrinking the process alone will give you a speed boost.

But it goes further than that. Chips are cut from a wafer. The cost to make that wafer is (for the most part) constant. So if you can only make 20 or if you can make 2000 chips from that one wafer, it ultimately costs the same. But then that means the more CPUs that can be made per wafer, the per-CPU cost drops.

So you get a more power efficient, cooler, faster and cheaper chip when you shrink the process. The entire semiconductor industry is so dependent on this idea that it invests billions into it every year because it is so vitally important.