Why might an administrator-level user be unable to see the Layouts or Templates nodes in the content tree?

An administrator-level user might be unable to see the Layouts or Templates nodes in the content tree because the 'Hidden items' check box has been unselected on the View tab of the ribbon. In Sitecore, the content tree can include items that are marked as hidden, and these items will not be visible unless the user specifically chooses to display them. If this option is unselected, all hidden items, including critical components like Layouts and Templates, will remain concealed from view, even for a user with high-level administrative access.

Given that Sitecore allows users to filter out certain items from their view to maintain a cleaner interface, it's essential to ensure that the 'Hidden items' checkbox is activated when an administrator needs to access all elements within the content tree. Therefore, this setting directly impacts what an administrator can visualize in the content tree and is the main reason, in this context, for the inability to see specific nodes.