The interest in contacting the spirits of the deceased was boosted by the American Civil War, the dicovery of the electromagnetic spectrum, and again in the bbeginning of the 20th century, with the 1st World War and the developement of the vacuum tube, and electronic circuits incorporating them. The division between science/technology and the metaphysical/paranormal wasn't really made yet, and for instance both Edison as well as Tesla were trying to develop a way to contact spririts by means of some kind of rado technology. Spiritis/spiritualism. psychic mediums and seances to contact the dead were in vogue at these times and the kind of things hadn't been sorted into the category of pseudo-science and fraud.
It seems like performances with the theremin and the Ondes Martenot back in the 1920s were often styled somewhat like a seance and/or a religious ceremony, and given a touch of mystique.
The connection between spirit(ual)ism, feminism and women's equal rights, the suffragette movement, and many of the early pioneers of electronic music being women is quite interesting as well.
So it might partly also be due to another Zeitgeist and worldview between the early 20th century and what we find ourselves in nowadays.
I wouldn't call the D-Lev "a digital imitation" for instance, although for the Moog Theremini the argument could be made I guess and perhaps even for the Claravox as well, but I think those has their place too, perhaps as an introduction to the the touchless space-control-interface and to wet the appetite.
Personally I'm still especially happy with my Subscope handcrafted all analog theremin.