Drivers simply fail to recognize the motorcyclist's right of way.
Some motorcyclists may feel that drivers deliberately choose not to see us. They feel that drivers resent us because of our agility, acceleration, or designer leathers. Others suspect that some car drivers must be anally retentive psychopaths who compensate for their fear of flying by driving to kill. In the urban rain forests of LA or New York, that may be true. But elsewhere, most drivers really don't see motorcycles.