Fuel consumption in a tractor depends on engine load and hours run, not on distance covered. In fact, tractors often run PTO (Power Take-Off) attachments, like rotavators, pumps, threshers or more, while barely moving at all. In that case, km/L would be completely meaningless (you would technically get infinite km/L while stationary!), But L/hr still makes perfect sense.

Cars, on the other hand, are bought to travel from point A to point B. Their entire purpose is covering distance, so the natural question is: "How far can I go on one litre of fuel?" The metric km/L answers that directly. Whether you're on a highway or in city traffic, distance is the variable that matters to a driver.

The unit simply follows the purpose, tractors work, cars travel. So tractors measure fuel consumption per hour, while cars measure it in kilometres per litre.