Final answer:
The increase in steam elevator production was primarily due to the construction of tall buildings, such as skyscrapers, facilitated by the development of steel girders and the invention of the electric elevator.
Step-by-step explanation:
According to the provided excerpt, an underlying cause of increased steam elevator production was the construction of tall buildings. The development of steel girders that could support more weight than traditional materials led to the ability to construct buildings higher than the previous limit of 10 to 12 stories. The demand for taller buildings, mostly in the form of skyscrapers, made the elevator an essential technology. The Otis Elevator Company, led by inventor Elisha Otis, installed the first electric elevator in 1889, fuelling the skyscraper craze and allowing developers to build and market prestigious real estate in the crowded hearts of cities.