It's because people have no idea that anyone today would actually shave with a straight razor, and even if they thought you might, they wouldn't know what factors make the razor usable. They don't assign any practical value to them. Since they assume the value is almost solely based on the novelty or the rarity of the straight razor in general, what difference should it make how much hone wear is on the blade or whether or not it has been rescaled, etc. A broken blade will be worth almost as much as one that has never been opened
That's my theory