Fair question. Me and others wrote about it here 🦄 If Wishes Were Unicorns: Why Asana Might Not Have Implemented that Feature Request (and other thoughts about Asana feature development and product strategy)
To summarise: each feature has a cost. And building a chat would be very expensive. So if I consider that your idea will require a lot of resources, make the tool harder to use or adopt, I might want to argue against it.