why dont wealthy people tip their pizza drivers???

As someone who recently started delivering pizzas I have noticed something very peculiar. The more affluent the house the smaller the tip. While this is not absolute, I have received the occasional $5 from some of the nice homes, it is almost expected to either get stiffed or to get 2 or 3 dollars from quarter million to 1/2 million dollar homes. In steady contrast when you go into the lower income areas the tips are almost always 5 and above. For the record, if you are not tipping AT LEAST 5 dollars to your pizza delivery guy he is losing money coming to your home. If your excuse is "Well he is being paid an hourly wage" yes we are 4.25 an hour to cover gas, insurance and car air fresheners to get the nasty smell of pizza out of our cars!! Think about it, the driver packages your order gets in his car and brings hot food to your door and you cant throw him a five or better for his hard work? Unless you are indigent, your shame at handing the pizza guy 2 or 3 dollars is and should be palpable! You should hand the driver 3 dollars with a bag over your head to hide your shame. But this is just one drivers perspective...what do you think?