Rubber tires aren't new, they've been around for 120 years. If there has been an uptick in IBD in the past few decades that didn't exist for the first 80 years of the 20th century, you'd have to suspect a number of different things before tires.
Also consider the expansion of the US highway system (starting in '56), increased freight trucking, popularity of tuning / high performance cars etc. I'd imagine more tires are getting shredded into the environment than at any point before the 80's, even with improvements in tire compounds.
Take a look at a 1950s Coup de Ville, Buick Roadmaster or any other famous models from that era. All pushing 4K, sometimes 5K pounds.