A tree data structure is a favorite of computer engineers (especially in job interviews!) Trees elegantly describe hierarchies with a parent-child relationship. You can find user interfaces (UIs) expressed as trees everywhere. HyperText Markup Language (HTML) and the Document Object Model (DOM) are trees. UIViews and their subviews are trees. The Android Extensible Markup Language (XML) layout is a tree. While developers are subconsciously aware of this data structure, it's not nearly as present in the foreground as it is with Flutter. If you do not live and breathe trees, at some point you will get lost among the leaves.
This is why managing your widget trees becomes more important as your app grows. You could, in theory, create one single widget that is tens of thousands of layers deep, but maintaining that code would be a nightmare...