Due to the rampant "Piracy" present during the early days of the Amiga (and today apparently), most software companies resorted to creating their own versions of copy protection to prevent everyone from copying the floppy disks and distributing them to all their friends at the Amiga User Group meetings which were all over the place.
Piracy didn't kill the Amiga, but it sure pissed of a great many software companies that could not make their money back from Amiga programs they produced. It is easy to see why so many of them left for the land of Windows where it did not matter if a hundred thousand users pirated their program because another 500,000 users would purchase it and they would still make ten times the money they would have if they had just wrote programs/games for the Amiga.
So, to answer your question, the NDOS disks are probably copy protected and must be booted from directly, not loaded from Workbench.
