Why don't auto makers make a gas Gauge with a Numeral Digital read out rather than just lines?

We all know that our cars have a basic gas gauge that has F for Full,line for 3/4, Half, 1/4, and E for Empty. Why don't we has a gas gauge that is a Digital Number that reads as follows? 13 Gallons 12.5, 12, 11.5, and so on. At least this way you know exactly how many gallons your car really has in it rather than relying on a needle and lines that can be inaccurate and break or get stuck. Is it a conspiracy With the Oil companies to keep people filling up their cars more than what would be needed? Or is it just impractical and to Expensive and would add to the cost of a car?