Letting them go home means risking having less people in the office when the manager's boss shows up, which will lower the manager's prestige, and risks harming

Letting them go home means risking having less people in the office when the manager's boss shows up, which will lower the manager's prestige, and risks harming morale of the other employees. Giving them more work risks having their department fail if the employee leaves for any reason. Subtly encouraging them to waste time is the safest choice.