Dusk-to-dawn lights may stay on due to various reasons. One common cause is an obstructed or mispositioned sensor. It's important to ensure that the dusk-to-dawn sensor is properly positioned and not blocked by objects such as branches or debris. Additionally, a faulty detector or switch can also contribute to this issue. Power or wiring issues should also be considered, as they can disrupt the proper functioning of the dusk-to-dawn lights and result in them staying on.