Because it isn't road hazards. It's junk tires. The st tires are notorious for blow outs. My son has a Rockwood 5500 lb TT. Two years ago I replaced all the bearings and he took it to Discount for a set of new Carlisle recommended by them. He also wisely bought the warranty. Within a few months he had 2 blow outs. The second summer he had two more blow outs. He doesn't drive over 65 and keeps an eye on the pressure. These are supposed to be the new and improved Carlisles. They are rated at 1,870 lb x 4 = 7,480 and they cant carry 5,500 for a few months?
I bought a new single axle utility trailer rated at 3500 lb. It has some strange name Chinese tires rated at 1800 or so. I was hesitant to pull it across the country but it does have a few advantages that may let them live longer.
I drive 60 mph and never over 65
Always travel during cooler temps
Dont have the side shear forces of a tandem axle trailer
Only loaded at about 2,500 lbs
Fingers are crossed and at about 5,500 miles.
I would never think of pulling my FW without having 16 inch LT's on it.