It was for an upgrade. When I ordered my Librem 14, there was only the 4-cell battery at the time, which only allows for one included NVMe drive. I wanted to use two NMVe drives instead, so I told Purism to not include the 4-cell battery so I could use the space for both NVMe drives.
Later on, when the 3-cell battery became available, I shipped the Librem 14 back to them to install it and the second bracket for the other NVMe drive, so it can be properly secured on both ends instead of just the second NVMe drive’s insertion slot.