Why does the change engine oil warning come on after an oil change?

The user is expected to change the engine oil on regular basis as the oil which helps in lubricating the engine and its various parts have a limited self life. Due to regular use it gets contaminated with metal parts and dirt, this harms the engine mechanism and needs to be changed. Thus, after the change of the oil it helps in understanding how far the lubricant will work and keep the vehicle mobile.