I think, it will stay like that. It is unpredictable, how different users want to sort their nested items, so it’s hard de define a default, that fits all needs.
For example, if you have parent pages and child pages, that share the same categories. Now you filter by category. If a child page has that category, but not it’s parent page - how would you nest it in the output?
This could be solved in an addon, that declares some common defaults, so it won’t break the behaviour for all users.