When we ask any "why", we're looking to learn what the cause is/was for <whatever>. In some respects, one could almost call the two concepts synonymous.
What is the reason for the reason?
We have to stop all explanations at some point. I prefer the empirical view that stops at the rock-bottom way-the-world-is. Evidence and rationality can only stave off ignorance for so long.
Why does an apple fall to the ground? The law of gravity.
Why is there a law of gravity? You got me. :perplexed:
In fact, even the belief that the "law" of gravity makes the apple fall rather than simply describing how it falls is a form of dogmatism. Most modern philosophers of science agree that the laws of nature aren't very much like human laws at all. The belief in supreme laws that govern the universe obviously has its roots in religion. So, it's no surprise that the many people in the highly religious West still cling to the notion of controlling laws, causes and forces.
All "why" questions are ultimately farcical. They only appear to be offering explanations but instead always point to still more "why" questions. What makes something an explanation rather than a description is purely psychological.
A law of nature is N( G, F) where N is nomic, and G, and F are universals.