There may be someone coming, seeing the door is closed, and just leaving a note for maintenance to fix it when you aren't around. They may also be using those

There may be someone coming, seeing the door is closed, and just leaving a note for maintenance to fix it when you aren't around. They may also be using those sensors to know if someone opens your door while you're out of the hotel and/or without an authorized keycard, which might mean a robbery attempt.