Competition for markets has led to a great increase in the rate of introduction of new designs for products, and increasing pressure is placed upon all concerned to produce at a lower price than competitors. It is therefore no longer possible to continue long-term production of a product once it has been developed to an adequate level of quality. In addition, considerations of economy, and the enormous increase in the scale of manufacturing, have led to heavy dilution of the skilled labour force formerly employed to produce quality products; and competition is further intensified as developing countries enter the market with competing products.
It is useful to distinguish between (a) poor quality from the perspective of the producer and (b) the user. One author distinguishes between custom- designed or built products and mass-produced ones. Custom designed dams, software, ships, financial investments, consulting work, etc., are different because there is no clear difference between design, production and delivery. They all happen effectively at the same time.
One can also distinguish between (a) poor quality products (b) deterioration over time in the quality of products and (c) poor quality not just linked to products but also services, research, etc.
If you like it, it fits and you can afford it, it falls apart the first time you wear it.
Quality assurance doesn't.