Another thing here is that everyone is visible in the frame at all times. Here you could even cross
the line without causing too much confusion, as the people facing each other would still all be visible in the frame.
But when you film dialogue in a way where you see only one character at a time inside the frame, then the line becomes even more important.
And notice how they lead you from one character to the next by letting the characters turn their eyes to them before they make the cut.