Are six year loans available for used cars ? No they are not. Only for new. That fact alone indicates that marketers acknowledge that in order to sell their new car inventories, they need to give the consumers more time to pay them off. This is unnecessary with used cars.
Such a necessity reflect a shift in the customer base, a decline in the number of customers who can comfortably afford a four year loan for a new car.
Again, your evidence does not support your assertion. Auto manufacturers do not get paid by the distributer until a new car is sold. For this reason, auto makers have an interest in getting people to buy new cars. "Better" credit terms, in the eye of the consumer, may make him purchase a car he otherwise wouldn't. It's not a coincidence that these "better" credit terms also mean higher profit-margins for the manufacturer.
To come back to your argument, you could just as easily argue that consumers are "poorer" because auto makers spend billions of dollars on advertising. If consumers weren't so poor, then cars would sell themselves, right?