One of the biggest values for any company is its Intellectual Property and SAP is trying to protect its Knowledge. As a result, most of the SAP Knowledge Base Articles are protected (gated). Only Users with S-user credentials have access to most of the SAP Knowledge Base.
But Crystal Reports is a separate case. It is a Client application that does not require a maintenance agreement, so a S-user ID is not provided to the owners of the application.
As an exception, SAP provided public access to all Crystal Reports related Knowledge Base articles.