This is done, drivers do get a route (EDD trace). Problem is that there's a min wage human (machines are too slow/expensive) with heavy time constraints who loads the truck. If they're part of the 1/3 that is a peak seasonal, don't care, or are pushed too hard by management, the load will be bad. Loading stop for stop is hard and has no incentive.

Most routes (at least here) have business stops which make up the majority of the bulk down the middle. If it's a resi route with a lot of irregulars (70-150lb packages, mattresses, etc) it'll be a mess.

The options to solve this are pretty much more trucks (there are none, and nowhere to put them after the "normal" seasonal increase), more drivers (hiring/training is an issue), making multiple trips (depends on distance from hub), or having parts of the route shuttled out.