Because the father -- one of the fathers of the Industrial Revolution, Adam Smith -- was convinced that human beings were by their very natures lazy, and wouldn't do anything unless you made it worth their while, and the way you made it worth their while was by incentivizing, by giving them rewards.
En av grundarna till den industriella revolutionen, Adam Smith, var övertygad om att människor var naturligt lata och inte skulle göra ett dyft om man inte gav dem en anledning, och man gav dem en anledning genom att motivera dem med yttre belöningar.