Why are you required to brake now?

You answered correctly. You are required to brake because of the motorbike. In this situation, the motorcyclist is waiting at the side road and wants to enter or cross your priority road. Even though you have the right of way, it is important to be prepared to brake or slow down, especially if there is any doubt that the motorcyclist might not yield as required. This is part of defensive driving—anticipating that other road users may make mistakes—and it helps prevent accidents. The van and cyclist are not reasons to brake here, based on the traffic situation shown. Remember: always be ready to adapt your speed if there is any risk that a waiting vehicle might enter your path.