

Lifeguards have very short periods of diligence before they take mandatory breaks in an extremely controlled environment. Train conductors operate on grade separated infrastructure. Security Guards do not have to take split second action or die.
Putting a warm body in a mind-numbing situation and requiring split second response to a life or death situation at a random time is a recipe for failure.
Lifeguards take breaks every ~20 minutes, not just to look down or zone out, to get up and move around. And again, are in an extremely controlled environment looking for a very small number of specific problems.
Elon is making programmers sleep at their desks.