Thanks for the suggestion. In the official Google app, you could choose either the default view or the "sort by date" view. If you choose the latter, all subtasks will be flattened, because it's possible for parent and children to have different dates. You probably never do this, but there are people who do. If you think about it, it's impossible to maintain hierarchies in such cases.
This extension tries to simulate exactly the same two views as the official app - the normal view and the "sort by date" view, so that what you see in this extension mirrors what you see on the phone.