This is because it is RAW.
RAW is not a file format, RAW is how a drive is shipped. In other words, the drive lost the partition tables. If you are VERY lucky, you might be able to recover your data using recuva, after recovery to a known good drive, I suggest sending the 3TB drive back under an RMA because once it looses the file system, IMO, the drive is not reliable, and 3TB is a lot of potential data loss.
Curious, does this 3TB drive use a fancy SATA controller that shipped with it for use? If so, that is another possible reason your drive is showing as RAW. When 3 and 4TB first came out, they had to ship the drives with special PCIe SATA controllers since most systems would not properly recognize the drive. The drives would default to less than 1TB of storage space due to not having the special controller. Hooking these kind of drives (the ones that required a special PCIe SATA controller) upto external enclosures causes some serious issues with data loss.
So, put the drive back into your PCI, find Recuva, make sure it supports your SATA controller, load it up, and see if it can scan your drive for lost files. Do NOT create new partitions/format/store data on this drive till your data is recovered. Doing that will result in most cases damaged/corrupted/unrecoverable data.