I don't find it so.

If any given post/article can stay on specific topic (which it most certainly does almost all the time) then why can’t the collective group of people do the same, particularly when the technology is specifically designed to achieve that goal?

I reject the premise that "the technology is specifically designed to achieve that goal". I believe a good conversation does branch out and lead one into a myriad to topics, where those topics relate back to the primary topic.

If conversations here were routinely jumping to something completely unrelated, then I could see your point. But I don't feel like I see that, at least not in the conversations I participate in.