Getting a machine to learn to speak like a human being has been a holy grail for computer scientists as well as linguists – of all the things which machines can mimic human behavior, holding a conversation has been a challenging ordeal. The quest to make such a machine which can chat with us humans (or a chatbot, if you will), has had many different approaches, and while none of them work perfectly, it is important to be aware of them - and pick and choose which kind will be the best for our purpose!
As for why we would want to build them – chatbots are increasingly used by businesses; both to help customers to answer basic questions, as well as for building more complex personal assistants. It is also becoming increasingly easier to build such chatbots, and using open source tools.
There are many motivations to study the art of conversation for machines...