In the monolithic component example, you started off with a single component that was entirely focused on a feature. This means that the component has very little utility elsewhere in the application.
The reason for this is because top-level components deal with application state. Stateful components are difficult to use in any other context. As you refactored the monolithic feature component, you created new components that moved further away from the data. The general rule is that the further your components move from stateful data, the more utility they have, because their property values could be passed in from anywhere in the application.