The "super" products are more expensive to produce, likely, given their higher retail prices.
They have more refined or superior additives one supposes. For sure, a quick comparison shows higher flash points (good in hot weather) and better cold weather flow.
Not unlike a straight 20w oil versus a 5w-20 oil. Both work, but I'll bet you pay more for the 5w-20 multi viscosity oil.
In spite of the bias of certain southern dealerships, and despite the silly packaging Kubota did with the SUDT by putting snow flakes on the bottle reinforcing this silliness, the SUDT is merely a low viscosity, multi-viscosity fluid. John Deere and many, many others offer various grades of tractor fluid.
But, if you're a dealer in the south, why bother with having to stock it and fuss with it. Would your customers pay more, as they must for the "super"? Doubtful. Or at least, not enough of them.
Now, back to our regular programing, as they say.