Their boss wants them not to stop working but (I imagine) could not care less if they cry or smile as they work. Do you agree it would be harder for them if they were required to smile and make small talk as they worked? If you want another example of not having to do emotional labor, think of a rock star who gets away with throwing tantrums at his manager or quitting halfway through a show - zero emotional restraint required.
Workers cannot express (unrestrained) anger towards their boss. Can you? Rock stars cannot express anger towards their audience. I mean, I suppose they can, but it increases the chances of unemployment.