Being able to predict what other drivers are going to do is probably the biggest part of driving or riding safely. It is hard to teach that skill to others though, because most of us don't understand how we know what another driver will do - it's usually "just a feeling", and that only comes after years of driving experience.
People only have a certain amount of attention that they can devote to tasks, and predicting what other people will do is a very subtle, complicated task. Riding a motorcycle is also a complicated task, so trying to learn both skills at once means that neither skill will have your full attention. If you are spending a lot of thought on shifting, balancing, avoiding potholes, etc, then your attention to other traffic will suffer. For this reason, most people will recommend spending a few years in a car first to get a firm grasp of how to interact with other drivers before hopping on a bike. The dynamics of controlling a bike are considerably more complicated than controlling a car.