Is it bad engineering? Or do people lack intelligence?

Complexity causes 50% of product returns: scientist 

Half of all malfunctioning products returned to stores by consumers are in full working order, but customers can’t figure out how to operate the devices, a scientist said on Monday.

My vote is that people are generally less likely to exert the effort required to learn how to do something correctly. Want proof? Go drive down the street and watch people (barely) operate their autos well enough to get where they are going.