I think probably it has something to do with that size being too tall a sidewall without enough tread to maintain a load range "e" and a higher load rating. On paper i think it would be the perfect highway towing tire with excellent aesthetic value but in the real world that tall a sidewall with only an ~11.5" wide footprint would probably cause some sidewall flexing, even with a 10 ply sidewall, when loaded heavy. I have no scientific basis for this line of reasoning, just the thoughts of a science nerd...lol