Here's why:

* Concrete is a manufactured material: Concrete is a mixture of cement, aggregate (usually sand and gravel), and water. It's created through a process of mixing these ingredients and letting them harden.

* Sedimentary rocks form naturally: Sedimentary rocks form over long periods of time from the accumulation and cementation of sediments like sand, silt, and clay.

While concrete can be used to build structures that mimic the appearance of sedimentary rock formations, it is not a naturally occurring rock itself.