I've often wondered how with the advanced medical science of the Federation how they can, for instance, revive practically dead people, but not create a communication device for Pike (or any of a number of people in the background of Lower Decks) more advanced than a blinking light.
One theory I had recently is that somehow, Pike (and people with similar conditions) received most of the brain damage in Broca's Area, leaving them able to understand speach through Wernicke's Area but unable to produce speech. The chair thus might be a replacement for Broca's Area, but primitive in comparison to the original, biological one. (And further, perhaps the Talosians are able to simulate a human Broca's Area when Pike is left in the illusion on Talos.)
Good theory - it's been a long time since I studied brain anatomy, but hyper-specific brain damage might be the only way to truly address Pike's situation as depicted in "The Menagerie".