Smaller trucks would mean more drivers (which are already hard to find). More drivers mean more costs. You would basically penalized logistic companies either way just for them to do their job: Bringing goods into the cities.

Someone else suggested to go by rails. Hardly feasable, as one would have to turn half the cities into railyards. And any kind of train can only operate efficiently because of sheer size. Which means: problems with small curve radiuses. Which an inner city most likely will have to have, unless you only fit the major roads, and move the goods for the last few hundred meters by whatever means.

There is a shitload of catch 22's in this whole story - cities evolved to what they are and how they worked over a long time, and changing them will cause mega efforts.