Other people in your organization want to integrate with your service, library, and other tooling. It makes sense to provide documentation to help with these integrations.
Languages also have fairly standard documentation libraries like Rdoc or Yardoc for Ruby, Pydoc for Python, and Godoc for Golang. Libraries may also generate their own documentation in some other way.
One important thing to note is that most documentation libraries assume the end product is at the root of the domain (not in a folder). This means that https://foo.docs.myorg.com would work, but https://docs.myorg.com/foo/ would not work and break links to other pages and assets. For this reason, it is recommended to have a simple webserver with a wildcard certificate for *.docs.myorg.com