It’s because the system has to rely on visual cues, since Tesla’s have no radar. The system looks at the tail light when it’s dark to gauge the distance from the vehicle. And since some bikes have a double light the system thinks it’s a car in front of them that is far away, when in reality it’s a bike up close. Also remember the ai is trained on human driving behavior which Tesla records from their customers. And we all know how well the average human drives around two wheeled vehicles.