It's not silly question, actually for lot of developers List is default thing when it comes to collections.

Arrays and List serve different purposes, List is more flexible and its built on top of Array but adds helpful features like resizing and extra methods while arrays are simple way to store fixed-size data and are very fast and memory-efficient.

The reason why we teach arrays is that it helps you to understand how data is stored and managed in memory, It's foundation to understand how more advanced data structures like List works.

The reason why both exist is that sometimes you need the speed and simplicity of array and other times you need flexibility of List.