The lack of palletization on Target's trucks seems inefficient at the store level, but may be justifiable at the company level, since Target owns its own distribution centers:
* Trailers are 9-10 feet high, so a fully palletized truck would (a) Have very tall unwieldy pallets, and you'd have to carefully order things so boxes on the bottom don't get crushed, (b) need racks or something similar to hold multiple tiers of normal-height pallets, or (c) be half-empty
* Even with the current process, getting boxes off the truck is not even close to the bottleneck. When I worked at Target, 2 people threw boxes onto rollers, 5-6 people sorted the boxes onto pallets organized by area of the store as they went by, 2 people rolled those pallets onto the sales floor and threw each box in front of the appropriate aisle, and ~20 people opened the boxes and stocked the shelves. The 2 people unloading the truck could always keep well ahead of the 20 on the sales floor.
* An alternate strategy might be to sort the boxes into pallets by store area at the distribution center rather than at the store. You might get some economies of scale out of doing this process for 100 stores at 1 distribution center, but it may still not be worth it to put all that needed floor space, latency, and congestion in what I imagine is already a very congested point in the supply chain. Better to distribute that part to the endpoints, since you already have 100k square feet per store to work with that's just sitting there while the store's closed.