Why are you not permitted to now overtake the bus driving ahead of you?

You answered correctly. When a bus ahead switches on its hazard lights at or near a stop, German traffic law requires all following vehicles to be extremely cautious. Overtaking is not allowed because passengers, especially children, might be crossing the road. Additionally, with a motorcycle riding closely behind and preparing to overtake, attempting to pass the bus would be dangerous and unpredictable. Both the hazard lights of the bus and the presence of the motorbike mean you must not overtake here. Remember: Always slow to walking speed and never overtake a stopped bus with hazard lights activated, and also pay close attention to other vehicles that could create additional hazards.