The relationship between pages and menus is not immediately obvious for new users. How to sort menus, how to remove menu items when you've deleted a page, these are questions that might cause confusion for users when they are handled in two different sections.
Every theme has a "base menu" that's in lockstep with the pages you have, even themes that don't support multiple menus.
The "Base Menu" uses the menus section. If you delete a page from "Pages", the menu item is deleted as well. When you sort a "Base Menu", this is reflected in the "Page Order" page attribute.
The "Page Attributes" panel is revamped to hide the "Page Order" option.
This approach has the following benefits: