Not "desires". Needs. A car is a necessity unless you live in Washington or Manhattan. You can't choose not to have a car.
New cars have to compete with used cars and leases. If new cars could only be sold at 4 year terms, most people, balking at a $400+ monthly payment, would settle for a used car. So the six year term is an attempt to accomodate new car prices to the monthly budgets of most Americans.
What will you say when it's 7 or 8 year car loans ?