The exploitation goes both ways. Consumers don't necessarily depend on the sale, but they take advantage of it because it's there the same way businesses take advantage of consumers because they know they will go out and spend a lot of money if the prices are low. Neither side is completely at fault, obviously, but I don't think this is an example of something being wrong with humanity.
This isn't directed at you specifically, but it is a lot easier to sit on a pedestal and preach about living within your means when you've never had to struggle to do so, as is the case for most kids/people on ns.