I've wondered that also... however I've always felt that one of the good things about the Steem platform is that ancillary conversations happen elsewhere, like on Discord (or Twitter), while the feed is restricted to posts, but then the comments on post allow for contextual conversations to happen there.

Do we really need a 'chat' to be on the blockchain? I'd say no, given the nature of what blockchain is.

Strange how we never had an in-house chat app though... I know Steem-chat, but never used it TBH. Discord seems easier to use, unless it's my imagination.