While it does relate to price discovery--i.e., some folks just aren't willing to pay for an additional unit of quality at 10x--my theory is that the decline in quality is another hidden form of inflation. Thing continues to cost X even though regulations have increased costs Y, ship production to China and scrimp on the inputs. (Or have market forces do that for you.)
Problem is, you pay 10x for shirt that is made in the same factory as the cheap shiry, just has a different logo.
This has become a sort of unintentional skill in the ecommerce era. Everyone is using china, either the actual "first party" brand that is really just ordering bulk from china and reselling it stateside, or the various clones of that brand. The skill then becomes feeling out which of these various products and clones are coming from the better option of the couple chinese manufacturing companies everyone is using, then buying whichever of these is going for cheapest and least shipping headaches. Usually also if a product has been out for a couple years, there's an initial version widely available then an actual 2.0 version that solves a lot of the issues in the first, more sturdy at now known failure points, etc. That 2.0 version actually usually circulates in the no name brands for a little while before the "first party" brand eventually picks it up for their own line.