When the tires are off the ground being held up by stabilizers you致e got maybe a ton of tire and fluid hanging on the axle. And it痴 just a static load. No bouncing, rolling, or side pressure. When the tire is in the ground you致e got 3 tons of machine sitting on them shared between both of them.
I'm not saying you're wrong, because I don't know. But it's not entirely an apples to apples comparison either. The weight applied to the axles while sitting on the wheels is applied one direction. The weight of loaded wheels hanging off the axles of a raised tractor is applied the opposite direction. Maybe they just didn't design it for that?