Another interesting aspect of this, which I remember specifically from reading MS-DOS manuals in the 90s as a kid (I was an incredibly fun 12 year old) is that this choice was an intentional one done in the name of flexibility. These device names were correctly written with a colon, but you are allowed to omit the colons. For instance:

copy con lpt1

And

copy con: lpt1:

were interchangeable. If they’d chosen to not save users keystrokes and force colons when referencing devices, I’m not positive, but I think it would have eliminated the need for many of these reserved words in file names in general.

Also, side note, the “copy con outputfilename.txt” idiom is one that I still can’t ever remember how to do the equivalent on UNIX/Linux!