If one implements a low-level code, then one has freedom to pick good data structures. But when writing GUI apps there is simply no such freedom as data structures are already defined by libraries.
For example, a GUI framework typically uses a notion of widget tree that is fundamental to the library design. But the end user UI does not look as an arbitrary tree with deep nesting. It is easy to see that using a tree for this leads to extreme denormalization of data. Normalizing that to a relational form should remove a lot of duplication and code (often hidden) to synchronize that duplicated state. But try that with a popular framework. It is not doable in practice. So one sticks with tree architecture and its inefficiencies.
For example, a GUI framework typically uses a notion of widget tree that is fundamental to the library design. But the end user UI does not look as an arbitrary tree with deep nesting. It is easy to see that using a tree for this leads to extreme denormalization of data. Normalizing that to a relational form should remove a lot of duplication and code (often hidden) to synchronize that duplicated state. But try that with a popular framework. It is not doable in practice. So one sticks with tree architecture and its inefficiencies.