The scope and intricacy of production processes had expanded to the point that they required planners and coordinators to ensure that all the pieces came together efficiently and effectively. The rise of managers as the thinkers who would devise such blueprints—and the reduction of workers to instruments of implementation—seemed to follow as a natural consequence. Reductionism lay at the heart of this drive for efficiency.
All of this is true, and also the fact that markets had become larger (the entire US) which necessitated scaling production.
