Here's why:

* Sedimentary rocks are formed from the accumulation and cementation of sediments, like sand, shells, or mud.

* Melting changes the rock's composition and structure. This process occurs deep within the Earth's crust or in the upper mantle.

* Metamorphic rocks are formed when existing rocks (including sedimentary) are transformed by heat, pressure, or chemical reactions.

It's important to note that the type of metamorphic rock formed will depend on the original sedimentary rock and the specific conditions of the melting process.