If you adjust for inflation, 300 1976 dollars correspond to 1442 current dollars. I'm not saying they're not worth it but it's something that people always forget it.
You can still buy clothes that will last decades, they're just more expensive than the average person is willing to pay. Especially considering the length of time that something stays fashionable.
ETA: I just looked in my closet because I have a Sears dress shirt from the 70s. It is thin enough I can easily see my hand through it.
When the collars wore out, I'd remove them and sew them in upside down. You just can't kill BB shirts made up to around 1980.