Natural language is the lazy user interface (2 days ago) https://news.ycombinator.com/item?id=34549378
Chatbot is often a useless, unintuitive UX for solving problems. We already know how most websites work, so it's easier to navigate to the intended resources with a few clicks rather than typing uncertain questions.
It's useful - but it's only better if a given website lacks such a good faq or equivalent.
Another thing to consider is even for the sites that have real humans standing by to chat, the chat can be useless when the company basically doesn't want to their low-level any more leeway than the site's normal forms/application allows.
I mean, I could imagine kinds of AI chatbot that could be very useful - a bot that could talk someone through the process of medium-level auto repair. But this seems to be also something well beyond the ability of current systems.
That doesn't mean they supplant motivated user interfaces; they're for different purposes.