You probably aren't using a good viewing spot to determine how many people use their SUVs to transport more than just the driver.
If people were using their SUVs to drop off the kids on the way to school, then I would imagine that when the driver got to their final destination the odds of being the only person in the car would be pretty high. Most teachers/adult students, probably wouldn't actually bringing their kids to the university with them, right?
My wife frequently goes to the gym after dropping off the kids at school. A lot of people see her with only one person in the car but that one spot doesn't really show all of the ways the car is getting used.