Because (at least 8 months ago when this post was written), that is where the conversation was happening. There since has been a huge flood of spam from many self-promoters of Steemit, but in recent weeks I have taken the job of cleaning that up. I can't say the conversation has started again, but that's what we are hoping will happen.
At this point SteemTrail is working on their own chat interface, and we will try to migrate when that happens.