from Chris again regarding this question: Most likely a supply issue. I take it to mean if there is enough supply from gpu maker to Dell, you can buy the oem gpu as a retail gpu on Dell external site.  case closed.
I'm looking to replace the graphics card in my Aurora R10 with a RX 6800 XT. However, NONE of the cards on the market can fit into the case (without removing the front fan) EXCEPT the Dell OEM versions. However, even though I'm an Alienware customer who paid a lot of money for a system, it is NOTORIOUSLY reluctant to accept or fit 3rd party upgrades. Dell wont sell it to me separately even though its the only 6800XT on the market that fits into the Aurora R10. This PC could have been a good buy if Dell would not think of 1000 tiny little things it can put into it that make it miserable. 
Why doesn't Dell sell separate graphics cards for the Aurora?