Why should you not overtake the moped rider in this situation?

You answered correctly. In a construction zone with a narrowed lane, several important rules apply. First, overtaking the moped rider could be dangerous because there is not enough space to maintain the legally required side clearance for overtaking two-wheeled vehicles. This puts the moped rider at risk of falling or being forced off balance, especially when space is restricted by roadworks barriers. Secondly, in zones with a 30 km/h speed limit and road narrowing, you are not allowed to drive much faster than the moped, making overtaking unnecessary and unsafe. All three reasons are valid and show why overtaking here would violate German safety rules. Next time you see a narrow construction zone, always consider both the legal clearance and the safety of more vulnerable road users.