Many (if not most) Meshtastic devices don't have a GPS receiver of their own, and also may not be paired with a phone app to supply location. So at least some devices would need to sniff GPS coordinates from traffic on the wrong band in order to know it's time to switch to the new band appropriate for the new location. Some amount of automatic reconfiguration could probably be made to work, but there would be serious limitations on how many use cases it could handle.