Here's a breakdown of why:
* Trade and Commerce: As Sumerian cities grew, so did their trade networks. They needed a system to record transactions, inventory, and debts. Cuneiform allowed them to write down these details on clay tablets, which were durable and could be stored for long periods.
* Government and Administration: With larger populations, the Sumerian government required a way to manage taxes, record laws, and keep track of citizens. Cuneiform provided a method for formal communication and record-keeping.
* Temple Administration: Temples played a significant role in Sumerian society. They needed to record offerings, rituals, and the management of their vast estates. Cuneiform enabled them to document these activities.
* Literature and History: While practical needs drove the initial development of cuneiform, it also became a tool for recording history, stories, and religious texts. This helped preserve Sumerian culture and knowledge.
In short, cuneiform arose from the need to manage a growing and complex society. It allowed the Sumerians to communicate effectively, record transactions, maintain order, and document their history.