Probably because those pages with just a single toggle requires more explanation about what the toggle does, and thus the explanation doesn't really fit with other settings.
Also, just like how it's easier to add a modal than integrate more state into the underlying view, it's easier to add a new view controller to your xcode storyboard for an interaction.
For example, as you note, you have space to describe it and add possibly more UI to the feature. And in a future pass, you can decide to fold it back in to the existing UI and solidify it there. But that pass isn't necessarily worth it.
