Here's why:

* Formation: Sedimentary rocks form from the accumulation and cementation of sediments like sand, mud, and organic matter. This process often happens in environments where life can flourish, like oceans, lakes, and rivers.

* Preservation: The layers of sediment that bury organisms can protect them from decay and decomposition, providing the conditions needed for fossilization.

* Erosion and Exposure: Over time, erosion can expose these buried fossils, allowing us to discover them.

While fossils can be found in other rock types (like metamorphic or igneous rocks), these instances are much rarer.