Bias ply construction and the rubber used is why IMO. The polyester belts are more forgiving than steel.
My first car was a 1970 Dart 4 door, that I bought in 2001. It had 11,000 original miles with the original tires on it. The car sat in a garage in Florida it’s whole life. My brother and I drove on those tires for a year before I could afford new ones. I was 14 lol I remember the new set of 14” tires were $118 installed out the door! Took me a year to save!