The primary reason is people don't start a thread about tires that didn't blow out and once a thread about a blow out starts, anyone who had a blowout jumps on board.
A distance secondary reason is maintenance. Your average passenger car gets driven every day and is well within the assumed design specs. If a tire is getting low, you generally notice it before it becomes an issue as the car feels different when driving. Also, tires wear out before they dry rot. With RV's on the other hand, they often sit for months. The drivers don't have that day to day feel to pick up quickly if something doesn't feel right and the tires usually die from age not tread wear.