Accidents are almost always the result of the negligence of at least one person. In most accidents there is at least one insurance company that gets involved by assigning an adjuster to the case.
Motorcycles are smaller and thus more difficult to see or more likely to be obscured by other vehicles or road conditions. Road conditions become major obstacles for a motorcyclist.
Due to their size they cause the most catastrophic accidents on the road today. There are several major causes of big truck/commercial vehicle accidents.