Probably because OTR only works when both parties are online at the same time.
Edit: that said I haven't looked at their solution. Maybe it has the same issues. Or worse.
Edit: that said I haven't looked at their solution. Maybe it has the same issues. Or worse.
My guess was they wanted to handle things like video chat and file transfer that OTR doesn't handle. But at least for video chat, I don't think it NACL will work out of the box either