JJ was asking about the "business mystery" and I can tell that it's no mystery at all....folks who buy LT tires for trucks will run them until they wear out...buyers expect performance for 50,000+ miles. On the other hand, 0% of ST tires ever wear out....they age out.
Look at the miles that most trailers travel over the 5-7 year life span of a tire: very few. Many, many trailer owners are weekend warriors, or even better, seasonal site users.
ST tires are made on the cheap, because their buyers don't expect to put many miles on them. Making them so cheaply means much bigger margins for the tire mfr. Tire mfrs have no good reason to encourage you to use an LT tire when they can tell you to buy an ST tires with 5x the profit margin.
ST tires work fine for the weekend crowd....but if you are traveling the country and putting on serious miles, you soon realize that the LT is the better choice. Look at the guys on here that are recommending LT over ST: these guys have towed trailers for thousands of miles and are speaking from experience.
Same reason that mfrs spec an ST tire: it's cheaper. Heck look at how tight they stretch the wires in your TT just to save an inch of wire.
So JJ and others, sorry to say that while this technical discussion has been fascinating, there is NO technical reason to use an ST tire instead of an LT tire. Mfrs only sell STs because they can get away with making them so cheap that they make huge profits on them.