"Surprisingly, the program has grown very little. People seem to run out of things to say or talk about rather quickly. Or maybe talking to an AI makes them uncomfortable."

I don't find it surprising. Back in the late 1970s/80s the growth in home computers and the porting and forks of ELIZA to various platforms introduced many to this concept. Later people made such programs available online. Your example resembles many of the early web based examples I remember, though all of those can recall had a submit button for the form. This looks antiquated, and to me seems unlikely to engage people these days (get off my lawn etc...) for any length of time. Even 'back in the day' people got bored once they became familiar with the algorithm. Tay had the plug pulled less than a day after launch when twitter users 'taught' it, perhaps unpopularity isn't a bad thing.