Because the resisitivity of the potentiometer (a non-linear volume iself) is in a non-linear dependency with the volume of the remaining fuel, its temperature, additives, sloshing and position of the vehicle to the horizon. But if you okay with 15% steps with +/-5% margin error, constantly showing a changing values - then sure.

I think what even if you never drive yourself you heard the stories how people managed to drive somewhere 'on a completely dry tank'. Tank wasn't dry it just not feasible to invest anything to show an accurate (<5%) reading.