It possible that you don't have the necessary privilege to view the body. The ability to read both the package specification and the body from all_source belongs to the OWNER of the package and any user with DBA privs. With Execute privilege on a package will let you read package specification.
Click on the plus sign to the left of the package name. When you open the Packages folder, you only see the spec. If you expand that package, you'll see the body and the spec members.