I think the problem is that it's also an interesting problem for humans. It's very subjective. Imagine a therapy session, filled with a long pensive pauses. Therapy is one of those things that encourage not interrupting and just letting you talk more, but there's so much subtext and nuance to that. Then make it compared to excited chatter one might have with friends. There's also so much body language that an AI obviously cannot see. At least for now.