It demonstrates CRUD at a small scale and is familiar, so we don't need to figure out what it's trying to demonstrate. It allows us to see how large the final product is and how much memory and CPU it uses.

It's not meant to be a showcase of what you can build with it; it's meant to give you the smallest complete application so you can get a good idea of what you need to know.

The thing that's meant to be a showcase is usually referred to as a Showcase or a Gallery.