Just a random stop for a minor violation. I guess maybe even out of boredom sometimes. Thats the wonderful thing about Officer discretion, you can bust butt one day and pull over everything that moves for simple insignificant things or you can choose to not stop anyone. The choice is the individual Officer's. I can tell you this with certainty i have found more drugs and arrested more people out of "clean" looking cars than out of the stereotypical bucket. I have written thousands of citations. The one thing that i hope people would understand is that it is NOT personal , no matter how much they make it personal in their own minds, it's not.
If you don't know the Officer then im sure you can bet he isn't just picking on YOU.
FACT: people do not like to get tickets, its inconvenient, costs money, costs time but it is necessary.
People dont really seem to mind until its them that gets one, thats really what it all boils down too.