Why did the sumerians change their writing from pictographs to cuneiform?

The Sumerians didn't actually "change" their writing from pictographs to cuneiform. Cuneiform actually developed from pictographs.

Here's how it happened:

* Early Sumerian writing (around 3500-3000 BCE) was indeed pictographic, using simple pictures to represent objects and ideas.

* Over time, these pictures became more abstract and stylized. As writing became more complex and needed to represent abstract concepts, the pictographs evolved to represent sounds instead of just objects.

* This led to the development of cuneiform. This writing system used wedge-shaped marks (cuneiform) created by pressing a stylus onto clay tablets. Each mark represented a syllable or sound.

So, it wasn't a sudden shift, but rather a gradual evolution. The Sumerians refined their writing system to become more efficient and adaptable for their increasingly complex language and needs.