Here's why:

* Weathering breaks down existing rocks into smaller pieces (sediments). This can be caused by wind, water, ice, or even plants.

* Erosion moves these sediments from their original location. Again, this is usually done by wind, water, or ice.

* Deposition occurs when the sediments are dropped in a new location, often in layers.

* Compaction and cementation happen over time, where the weight of the overlying sediments presses the layers together and dissolved minerals bind the sediments into solid rock.

So, the process of weathering and erosion plays a key role in creating the raw materials for sedimentary rocks.