Not sure I understand your math here. A car depreciates faster if it is driven (more repairs, needs to be replaced sooner). Just because I already own a car doesn't mean it's only the cost of fuel to drive it.
Tires, oil, brakes, belts, wheel bearings, transmission... With a mechanical system like a car there are lots of things which wear down with use.
Instead of trying to figure out the actual difference yourself, you can simply look at what people are willing to pay for a car which is the same year but has different amounts of mileage. The literal resale value of your car changes drastically depending on mileage, that is the actual unrealized cost most of these ride sharing services exploit.
