The additional risk of having dealers replace modules [instead of the full pack] is something I'd expect GM to avoid. It's a non-trivial process, and as others have pointed out, the opportunities for f*cking it up are plentiful. Replacing the full pack is relatively simple. Maybe GM will go through all the returned packs and re-purpose the modules if they figure out a way to verify they don't have the defects. It'd make a lot of powerwalls...That was how GM approached it initially. Based on the newest bulletins, it looks as though GM has thrown in the towel on that endeavor. They have listed ALL 2020-2022 Bolts in the same recall, and flat out said that battery packs are being replaced.
The decision to not open up the batteries is a good decision, IMO.