Why did D.W. Griffith begin making longer films after directing one-reelers?

Between 1911 and 1912, D.W. Griffith’s one-reel films grew increasingly complex. As he refined his narrative techniques and artistic vision, he realized that the standard one-reel format—which lasted approximately 12 minutes—was no longer sufficient to contain the scope of his work.12

He began experimenting with longer, more expansive formats to accommodate his increasingly sophisticated storytelling, which included structurally complicated narratives and massive production elements like large-scale sets and battle scenes. This transition culminated in his four-reel film Judith of Bethulia (1913), which allowed him to execute a vision that was not possible within the constraints of shorter films.1