What does where your coming from and going have anything to do with a basic traffic stop?

A few years ago I got pulled over for a back tail light out (I had no idea). I ended up just getting a verbal “fix it”.

But the cop asked where I was going, where I was coming from, and then follow up questions to my answers. None of which has anything to do with one tail light being out.

Why do they ask this? And how do you respectfully decline to answer?