Remember that the oil is designed for internal combustion engines and the lubrication requirements for internal combustion engines are different from those for firearms. Gas engines have many different tolerances than guns do and operate at very small temperatures and pressures. Therefore, oil is not the best lubricant for small arms.
Gun oil is designed to work well under the extreme conditions of firearms. The tolerance of firearms is much stricter, and the pressure and temperature are much higher. In addition, they must work in harsh environmental conditions, such as hot and dry, hot and humid, sub zero temperature, wind and sand, water, mud, soil, salt water, etc.