Motorcycles and cars have different mechanisms for transmitting power from the engine to the wheels. The way they operate in neutral is determined by these differences.
In a car, when it is in neutral, the transmission disengages the engine from the wheels. This means that the engine is not connected to the drivetrain, and thus no power is being transmitted to the wheels. When you release the clutch pedal in a manual transmission car or shift to neutral in an automatic transmission car, the engine is essentially decoupled from the wheels, allowing the car to roll freely.
On the other hand, motorcycles often have a different type of transmission called a constant mesh transmission. In this type of transmission, the gears are always in mesh, meaning they are always engaged with each other to some degree. When a motorcycle is in neutral, the engine is still connected to the transmission, but the transmission is not transferring power to the wheels. Instead, the neutral position in a motorcycle effectively disengages the gears in the transmission, allowing the engine to spin freely without transferring power to the wheels.
So, when you release the clutch lever on a motorcycle while it is in neutral, the engine continues to run and spin freely, but because the transmission is disengaged, the power is not transmitted to the wheels. This is why motorcycles can stay running in neutral while stationary. In contrast, cars disconnect the engine from the drivetrain in neutral, which stops power from being transmitted to the wheels, and the engine generally needs to be disengaged or stopped separately.