Selling a >$100 item without a cable is kind of dumb... Bargain hunters are happy to overlook problems, but if you sell a high-dollar item you should spruce it up if you can.
Most people who can appreciate a KB like this have an extra SDL cable around. (I have three Model M's, and just one cable I use for all of them. Unless you're buying KBs to resell them, how many of each kind of cable do you need?) And if an item's sufficiently special like this one, savvy sellers know that such details won't deter most people from bidding.
And
not cleaning up a KB often encourages people to bid because it implies a seller who's not up on values, and who may take considerably less than an item's worth. Some sellers may even do that intentionally, for the reverse-psychology effect... IMHO, anyway.
Prices have been in a slump for a while now. After that insane spike of about 2 years ago, I think that most people who wanted one now have it.
Having bought them when they were as expensive as possible, you mean. LOL