carry weight, drive long distances, etc etc. Trailer ST Tires will all fail at some point and since almost all if not all, are made across seas, they will get the blame. EVERY day a U.S. L.T. etc tire blows up on someone's car, truck, trailer or horse wagon. It's often not the fault of the tire, but the fault of overloading, not inspecting, rotating, or pure neglect.
I just drove my trailer across country (San Diego Cal to Raleigh NC) on tires that were put on a trailer in Indiana, drove to Cali and then I pulled it back across country (in AZ heat of 115, driving rain of TX and crappy roads in MS). They'd been on the trailer for 1.5 yrs.
Take care of them, replace before 5 yrs and keep covered. Don't over / under inflate and fill or check each morning before heading out. Simple recipe to controlling the controllable as much as you can.