Capitalism. Lower production cost and quality = higher quarterly profits. (Also lower wages by sending the factories to countries with cheaper labor like China, Mexico, Indonesia, etc) The quarterly profits are all that matters to the corps, not a quality product or customer satisfaction. Especially in aftermarket car parts since often you have only one company actually making the parts, and it gets labeled under many different brands.
Just look at even a name brand like Moog and their "problem solver" line. It used to be the best. It's questionable now, but still probably the best you can get for ball joints and tie rods.
If you have to keep buying the same part every 5 years instead of once every 20 years, it looks better on paper since they sell the part 4 times instead of just once. So it's in their best interest to make the parts awful so you have to keep buying them as a means of keeping their quarterly profits strong.
en.wikipedia.org