Why are you required to stop here?

At a "Give Way" (Vorfahrt gewähren) sign, you must yield to all vehicles on the intersecting road that have the right of way. In this situation, you are required to stop because the red car is crossing in front of you on the main road and has priority. The cyclist and the pedestrian do not require you to stop because they are not crossing your path on the priority road at this moment. The key rule is always to yield to vehicles coming from the left or right on the main road when you see a "Give Way" sign, until the crossing is clear and it is safe to proceed. This prevents collisions and ensures smooth traffic flow.