The light switch is a good interface to light up a room.

Putting in a motion sensor and removing the light switch forces the user of the room to meet the conditions the engineers of the room designed it for.

Providing a motion sensing light switch that has a manual toggle on it allows the user to correct for potential use cases that the automated sensor is not programmed to meet.

The best interface is the intuitive one, not a lack of one for the sake of saying it does not need to exist.