I will expand a bit on the previous educator's very good response.
The main reason why so many cars were produced so quickly each year was due to the invention of the moving assembly line at the Ford plant in 1913. The moving assembly line cut time at factories, for now workers no longer needed to leave their work stations in order to transport an item to another worker. They would perform their part of the assembly and set the product down on the conveyor belt, which would carry it to the next worker. This not only made factory jobs less physically demanding, it also made it possible for workers to talk to one another.
Demand for products was high in the 1920s, due not only to the rise in incomes, but also due to the increasing importance of advertising. Women, particularly young women, were employed in some factories to work on the assembly line. Their access to capital allowed them to buy some of the things that they helped to construct, including cars.
Young women in the 1920s demonstrated their independence by smoking, drinking, bobbing their hair, working, and learning to drive. As the previous educator mentioned, the ability to get in one's car and go to meet a beau allowed for a higher level of intimacy than was previously possible. Sexual mores had loosened, and young people—armed with money and mobility—had more freedom to define their own lives and plan their own activities.