Was this your only installment loan? If it was, it's likely that you lost a few points because of the change in your credit mix.
I lost 30 points when my car was paid off after it being declared a total lost and I'm guessing because my student loans aren't reporting yet. So as the above person stated if it was your only one that is why.
Its not a penalty for being responsible it is because you no longer have an installment loan. I went for 5 years not using credit at all, I was responsible but because I wasn't using credit my scores suffered greatly. Ultimately you have to decide how important those points are. Having said that you will get most of them back over time but to get all of them you will likley need a installment loan reporting on a regular basis.