A lot of people bash the chat app but assume other communication venues aren't being used, and this is actually a fantastic way to stay in touch with friends in-game. FB is a good if harsh example, it relies on your real name being used and other contact information, I can see people shying away from using that to contact people from an online game. I don't need that sort of thing and I've most of my in-game friends on discord, but I can see why some people who be thrilled over the chat functionality.