There are a few possible explanations:
-AWS is a complex platform with many products and services. It can be difficult to produce clear and concise documentation for such a large and ever-changing platform.
-AWS is largely geared towards experienced developers and system administrators who are already familiar with cloud computing concepts. The documentation may assume too much prior knowledge on the part of the reader.
-AWS offers so many features and customization options that it can be hard to know where to start when trying to document all of the possibilities.
That said, AWS has been gradually improving its documentation over the years, and there are some good resources available if you know where to look. The AWS Documentation website is a good starting point, and there are also some excellent unofficial guides and tutorials available online.