Hello BWJR,
The reason for this is because the G-RAID you have is a softwareRAID product. Meaning Apple controlled the RAID with Disk Utility. By formatting the drive outside of the RAID process it will split the drives back into being essentially a JBOD (Just a Bunch Of Disks)
This is likely due to being on Mac OS 10.11.x El Capitan. Apple removed the ability to manage RAIDs in their Disk Utility with the newest version of the Mac OS.
You can restore it back to a RAID with an older version of the Mac OS 10.10 or older or you can use the Terminal on your system to do it manually. There are a few articles out there that have been created because of this issue with El Capitan. HERE is one that we recommend.
