A diesel car typically produces more torque at a lower RPM than a car fitted with a petrol engine. You can think of ‘torque’ as pulling power and ‘RPM‘ as the engine speed or ‘revs’. If you’re reversing without using the accelerator, the speed of the engine will be low.
You’ll often find small ‘city’ cars fitted with petrol engines because they are light and don’t require much torque. Diesel engines are better suited to heavier and larger vehicles, vans and lorries because of the superior pulling power compared to petrol engines.
Due to diesel engines having greater torque even at lower engine speeds, it’s often easier to reverse in a car with with a diesel engine without having to use the accelerator.