Final answer:
Motorcyclists can be difficult to see due to their small size, ability to fit into blind spots, and quick maneuverability. Drivers may not be used to looking for such small, fast-moving objects, which makes active checking of mirrors and blind spots crucial.
Step-by-step explanation:
Motorcyclists are often difficult to see behind your vehicle because they have a much smaller profile compared to other vehicles on the road, such as cars or trucks. Additionally, motorcycles can easily fit into a vehicle's blind spots, areas where the driver's view is obstructed by the vehicle's structure or by cargo. Another factor that contributes to the difficulty in spotting motorcyclists is their ability to maneuver quickly, which can put them in unexpected positions relative to your vehicle, making it harder to keep track of their location.
Furthermore, some drivers may not be actively looking for motorcyclists, due to a lack of awareness or being accustomed to watching for larger vehicles. Therefore, it is vital for drivers to check their mirrors and blind spots diligently, especially before changing lanes or making turns.