Why may you not overtake in this situation?

You answered correctly because overtaking is prohibited when the overtaking distance is not clearly visible, which means you cannot judge if there is enough space and time to pass safely. This is especially important near curves, hills, or other situations where your view of oncoming traffic is blocked. Additionally, if you are only traveling slightly faster than the cyclists, overtaking can be unsafe and impractical, as it takes too long and may cause danger to you and others.

German traffic rules, specifically §5 of the Straßenverkehrs-Ordnung (StVO), require drivers to ensure an overtaking maneuver can be completed without endangering or obstructing others. When visibility is limited and speeds are close, you must wait until it is safe and legal to overtake. This protects vulnerable road users like cyclists and helps prevent accidents.