I also suspect that KTAC have a competitive advantage. Their true cost to replace or repair a tractor is significantly less than anyone else's - so they make money where others don't. Also keeps you in the family so to say - if you break your tractor you have to get another Kubota.
To be honest, all these things are things people inside companies say to justify what they're doing. Actually, they sell insurance because they need it with the financing, and someone thought it might be easier to make their own insurance than outsource it. And then once they had it, lots of people say "that's really good insurance" and so they start to think that's essential to their business model.
Actually, you don't have to get another Kubota. There are two different transactions when you suffer a total loss. First, they buy your tractor back from you at actual value at the time of loss. At that time, you are free to walk away with nothing or go buy a new tractor of equal or greater value within 60 days. If you choose to buy a new tractor, they credit the additional $$ towards the purchase of the new tractor.
If you bought a tractor for $25,000 and it was worth $10,000 when it was destroyed, they buy it back from you for $10,000 in the first transaction. If you buy another tractor, they give you $15,000 towards the new tractor. If you don't buy another tractor, you never see that $15,000.
They do not "replace" your tractor. It's your decision whether to replace the tractor or not and, if you do, what to replace it with. I chose to replace my L3901 with an MX5400 when mine was destroyed. I paid the difference between the two models (plus inflation).