I don't know enough about this to warrant going on about it forever. But all the reasoning under the sun doesn't change the fact that 90% of trucks on our roads are carrying one axle at any time - I'm not making this up - all you have to do is count them. I can see you'd want the biggest truck etc, but two tons odd being carried around for nothing still doesn't make sense - but then maybe if its needed for 10% of the time and that's when it pays for itself, perhaps it does...
As said I think your 90% is a bit dramatic. And will depend on time location and direction of travel.
If what you say is true 90% of Lorries are running around nearly 1/4 empty.