Goodyear Marathon Blow out

I had an blowout on 05-27-14 with Goodyear Marathon with only about 9,000 miles and about 4 1/2 years old, cover when parked. I am looking in to replacing all Goodyear tires with Carlisle. Just Google Goodyear Marathon blowout and you will not believe how many you find. I always checked tire pressure before driving, always set at 65 psi per the book. Trailer is about 2000 under weight. The temp was about 99f driving 65 mph, what the problem?????