Final answer:
Motorcycles can be difficult to see for drivers not only because they are smaller, but also their narrow profile, the auditory limitations of the Doppler effect, and unpredictable movement patterns which contribute to reduced visibility and perception.
Step-by-step explanation:
Besides being smaller, motorcycles are often difficult for drivers to see because of several factors. Firstly, due to their narrow profile, they can easily be obscured by other vehicles on the road, objects on the roadside, or blind spots in a vehicle's mirrors. Secondly, the Doppler effect associated with the characteristic sound of a motorcycle may not provide enough directional information to pinpoint its exact location until it is very close, especially on crowded roadways with noise pollution. Additionally, the movement patterns of motorcycles can differ from larger vehicles, making it harder to predict their next action and notice their presence.