The reason would be that not enough of them sell to be worthwhile. Simply going from your description it sounds like the kind of product that could be designed and set up for manufacture in a handful of hours. But then what? I have no use for the product and even if I were inclined to ignore the ethical considerations, I doubt that I'd sell enough of them to recoup my time.
The people for whom this would be most useful already have the resources to build it themselves!