This will save a lot of money over time. Last time I checked in any detail, electricity prices per mile of transport per ton were about 25% that of fossil fuel prices per mile of transport per ton, and that was three years ago. They should really move all long-haul trucking to electric as well, at least for the main trunk lines, and for city-wide delivery. Remote rural routes will likely be the hardest to electrify.
In shipping and logistics, time is money. Fuel can be dispensed in the US at a maximum of 10 gal/minute. Factor that against the largest charger you can find and see why the single cost difference doesn't matter yet.
> They should really move all long-haul trucking to electric as well
Reduced capacity from doing this requires additional vehicle time to haul the same amount of material. This isn't a single factor equation. Plus, over the road drivers sleep in their vehicles, and not always at truck stops. They're only allowed to drive for 10 hours, so it's not always as convenient as you might expect.
Consider the weight of 600 gallons of fuel vs. the reduced hauling capacity from using an electric truck and see why we're a ways away from this yet. Have no fear; though, the moment this is logistically favorable, they will switch.