It’s not capable of creating precise or maintainable documents (e.g. no styles as others have mentioned), which is a very common need that it’s adjacent enough to that lots of people use it for and then it fails.
That is, I should be able to define a "Code block" style that should appear in the same dropdown where google docs lets you select heading levels. When I select that "Code block" style, the app should format the selected bit of text according to the syte's definition. For instance: use a monospace typeface, apply some margins to this paragraph and paint a gray background on it.
Likewise, I should be able to update the style definition and all code blocks should update accordingly.
This is very basic functionality that has existed in word processors since... forever. Large and/or more complex documents are simply much much more painful to maintain/evolve without this feature.