“We launched this project to learn what people needed and expected of an assistant, and we learned a lot,” the company said in a statement. “We’re taking these useful insights to power other AI projects at Facebook. We continue to be very pleased with the performance of M suggestions in Messenger, powered by our learnings from this experiment.”

Further details here: https://www.theverge.com/2018/1/8/16856654/facebook-m-shutdown-bots-ai