Hi,
there may be several reasons, including software incompatible with 2004, hardware without drivers for 2004 or incompatible with 2004 and so on. Is there any more detailed description?
Why doesn't Microsoft inform us the reasons why our Windows 10 device is "not quite ready for update"? And, perhaps, at what point time our devices might evolve to be ready for update. Better yet inform each user why his or her particular device is "not quite ready for update" and what remedies might make it "ready for update". Maybe the remedies could be provided by Microsoft.