Why do you have to wait before the left turn?

You answered correctly. In this situation, you must wait for the motorbike before turning left because, according to German traffic rules, when turning left, you must always yield to oncoming vehicles, including motorbikes, that are going straight or turning right. They have the right of way. This ensures safety and prevents collisions during the turn. The car and the bicycle in this question do not have priority over you, so only the motorbike must be considered before making your left turn. Remember: oncoming traffic going straight or right always has priority over a left turn.