That's because the conductors were striking but not the supervisors, though, not because an automated line is inherently immune to striking.

I thought line 14 was stopped because of a strike some time ago but it was apparently just because of an incident, it might never have stopped because of a strike indeed. But that just means the employees that manage it don't strike.

Of course, because however controlled is the environment it runs in, all sorts of unplanned things can happen. A tyre blowing out. A passenger pressing the emergency stop button. A person or animal entering the tracks after defeating the barriers. Flooding in a tunnel.

All of these events need a fast response regardless of whether the hardware detects the problem and stops by itself or not, even if just to evacuate the people that are inside the stopped cars.