There are a lot of factors than can lead to the development of mixed economies. Most of them have to do with the protection of consumers. With no government influence, producers and make whatever products they want, no matter the safety. As economies develop, the government often take a higher share of total spending. Developed countries, such as in Western Europe, often choose to provide state welfare support, and greater government regulation of business and the environment.
The rise of economics programs in the 1920s and 30s came from the aftermath of the "Great Depression".