I think car manufacturer sets up a low fuel warning so high, not because some customers don't have fuel station for 100km in any direction, but for car health.

If you have 98% air in fuel tank, a water from air can be 'exported' (?) when ambient temperature is changing. It is not good for engine to run on water. Also fuel pomp may heat-up and breake. So cunning engineers put a pressure on you to fuel a tank earlier, than it is needed for simple driving another kilometres.

Quote from Jamexing :

As I've mentioned, the "low fuel" levels are VERY car specific. In this case , the car has a max level of 92 liters and a kerb weight of around 2 metric tons. BTW, 30mpg is pretty common among small and effiecient city cars. Fuel consumption is anywhere from 20mpg in heavy urban traffic to 26mpg on highway in the 2.5L diesel/turbodiesel Pajero's case. Note these are real life figures based on real life driving.

In this case, Mitsubishi erred on the safe side for obvius reasons. Getting stuck in a 2 tonne 4WD in the middle of an off-road adventure isn't fun.

One other reason could be that as car is meant for use at off-road conditions you can't get it to use all fuel if car is tilted to side so you need to have bit more fuel there to actually keep going.

Also car is very common in towing so there more fuel burns again. They have made very good thinking, not all manufacturers are as refined in details such as this.

One Toyota Hiace for example managed barely 80km on highway after light did lit and I even feathered throttle and saved as much as I could as I certainly did need to go that 80km to find gas station, fuel was out 100m before station so I coasted to pump.
It was diesel so naturally needed to take long starting after that, problem at least with older diesels is that if air gets into system it is quite hard to get rid of, modern ones have automatic air removing but older hand operated pump to do the job.