They may be more popular outside the US. Where I am a lot of big businesses still use facebook for their online presence, and use those very annoying chat bots as their support gateways. Really frustrating as a user, but that's the state of things where I am.
Chat bots are definitely still a big thing, but the value proposition has completely flipped.
Zuckerberg (and others) were pushing an experience for the user, where they'd be delighted by interacting with a humanlike support bot that could interpret their human request. The value would come from additional user engagement with the platform, and therefore ad revenue.
In reality, chat bots are a cost optimization technique for businesses, where they save money by paying support bot services in exchange for reduced support staff. Still making money for someone, but they're nearly universally a worse experience for the end user, and certainly not a reason why users would engage with the FB platform.
On the contrary, I've had much better experiences with chat bots than I have had speaking with customer support on the phone. With a chat bot, I can wait for a response and be notified immediately. I wouldn't even mind if they took multiple hours to fulfill my request. Staying on hold on the phone for even 5 minutes feels like hell.
An app is constrained by the functionalities it is designer for.
Chatbot, OTOH, is more flexible as it may be able to verify questions, offers nuanced answers, improves over time without changing the interface, and can be backed up by real humans if needed. If it is working of course, which can be a big if.
