Why are car mechanics so possessive?

Why do car mechanics think they own your car? I went to the car dealer today to get my oil changed. I will admit, I was a little over the 3000 recommended mileage since my last oil change. I've been busy. My car gets very good care. I get my oil changed on a regular basis. So what, I was a little over this time. When the service advisor put me into the computer and saw that I was over 3000 miles, he peppered me with all kinds of questions. "Have you been going somewhere else for your oil changes?" "Why haven't we seen you lately?"  I felt like I was talking to Tony from the Seinfeld episode, "The Bottle Deposit". I started to get worried. Was he going to turn me in? Was he going to kidnap my car like Tony did to Jerry's car? So what if I had taken my car somewhere else for an oil change? I did confess that a tire company was now rotating my tires. Why should I feel guilty about that? Geez! It's not that serious!