Clara Rockmore injured her bowing arm (her right arm) by pushing herself too hard. The whole thing came to a head on the eve of a performance of the Beethoven violin concerto in New York City. The damage was too severe, the problem was chronic, and she was forced to give up playing the violin altogether. She credits Leon Theremin with saving her artistic life.
Clara did give theremin lessons, although she never had any serious long term students capable of succeeding her as genuinely accomplished theremin virtuosos. One of the problems was that RCA stopped manufacturing theremins in 1931 so no new instruments were available for students in the early days. A few decades later, when theremins began to be manufactured again, Clara felt the available instruments were "toys" when compared to the theremins made by Lev Termen and RCA in the 1930's.
Why did the theremin fall by the wayside? Dawkins' theories of memetics aside, it is too hard to play and too limited. It is a "one trick pony". But as I have said before, that trick when it is done well, has a uniquely magical quality that is both astounding and moving.