The simple answer: It’s probably wearing out. Over time, the piston rings have likely become worn or stuck in their grooves, preventing them from sealing tightly against the cylinder wall.
Everyone who owns a vehicle knows you need to regularly check the oil level. (Note: If you do not know this, you’d better go check your oil.) A certain amount of oil loss is normal due to motor oil volatility – that is, boil-off due to the high-heat conditions inside an engine. I once attended