Why? Because frankly they just aren't good enough yet. In my experience they are too dumb to be useful and the process of interacting with the bot is just a waste of my time.
I also don't like when the chatbot interface pops up and starts interacting with me on an unsolicited basis. To me that's just like when I walk into a retail store and 3 seconds later somebody is in my face going "Can I help you find anything?" That is an experience that I also hate with a white-hot burning fury.
That said, I did have a good experience with an Amazon chatbot recently where I expected it to not work, and it wound up solving my problem after all. shrug