Because damage to the road increases by something like the weight increase ^ 4.
And HGVs really are the limiting factor on road design. We could ban SUVs maybe, we could ban cars and scooters and bicycles if various factions get their way, but if we ban HGVs - cities starve, in weeks if not days.
Which is why nobody wants this. Though we ought to be chasing efficiency there as well because as you wrote lorries are a significant contributing factor.