These things are much more complex than simplistic single-variable models.
Much of what you can buy today did not even exist 30 years ago. For example, trail running shoes more or less did not exist. Perhaps you could have had a pair custom made, at a high price, with the worse materials available at the time, but today you can them "off the shelf".
Even the many shirts I've received for free are very high quality and have endured years of abuse.
It is not actually more complex, you don't spend ~40% of CPI on apparel.
Do you have a source for this? Anecdotes along the lines of "they don't make 'em like they used to" are incredibly common but often fail to stand up to scrutiny.