Here's why:

* Composition: The Earth's crust is made up of different types of rocks. Continental crust is mostly made of granite, which is less dense than basalt, the primary rock found in oceanic crust.

* Thickness: Continental crust is thicker than oceanic crust. While the thicker continental crust is less dense, it's still denser than the thinner oceanic crust.

* Variations Within Layers: Even within a specific type of crust, there are variations in density. For example, sedimentary rocks are generally less dense than igneous rocks found in the same layer.

Here's a simple analogy: Imagine a bowl of cereal. The cereal flakes (representing different rock types) might be different sizes and have varying densities. Even though you're looking at the same "crust" (the cereal bowl), the density isn't uniform.

In summary, the Earth's crust has a range of densities, with continental crust being less dense than oceanic crust overall.