I do not know why they did not pursue this invention. At the time in 1965 Parker was starting to divest into different markets, so they were looking at their horizons. They had very sophisticated research laboratories, had experience with government contracts so I think the research labs were working on fantasy projects such as some of the fantasy pens from the future that we have seen.
Still, this voice activated writing machine, from some 80 years ago was waaaaaay ahead of its time.