Why did the American economy change from producer-durable goods to a consumer-durable goods economy?
This is a change that is generally said to have happened in the early 1900s. It is a change from a system where industry made things for other industries to use (things like railroad cars and rails) to a system where industry made things for consumers to use (like cars). This change happened largely because there was a rising middle class with more money to spend and because industrial techniques were making it cheaper to produce goods for mass consumption.
During the early 1900s, production became more efficient. This was the time when Taylorism was on the rise, making factories able to produce products more quickly and cheaply. This was also the time of the refinement of the assembly line by Henry Ford. Again, this made for cheaper goods, produced in large quantities. This allowed for mass consumption.
Mass consumption also came about because of increased demand. There were more and more people moving in to the middle class, partly because of the rise of industrialism that had been going on more or less continuously since the Civil War. These people had enough money (especially as goods became cheaper) to buy consumer durable goods.
So, during the early 1900s, there was more demand for consumer durable goods as people got wealthier and there was more supply as industry became more efficient.