One of the possible flags for a question is:
it is very low quality
This question has severe formatting or content problems. This question is unlikely to be salvageable through editing, and might need to be removed.
If I am not fully mistaken, flagging a question such adds it to the queue for low-quality posts, where the reviewer can select one of the following:
- Looks OK if nothing is wrong with this question
- Edit if you can fix all the problems with this question
- Recommend Close to recommend that this question be closed
- Skip if you are not sure and want to go to the next item
Ignoring the somewhat misleading help text for now, Looks OK and Edit are for questions that should stay open (but are possibly badly asked questions) and Recommend Close brings up the regular close dialogue, which contains the usual suspects, none of which is very low quality.
Now, to most low-quality questions one of the close reasons (duplicate, off-topic, unclear, too broad, opinion-based) applies. But all of these are directly available for flagging anyway; so there would not be any reason to take the long way via the low-quality queue.
If we suppose questions exist which should be flagged very low quality but to which no close reasons apply (which is debatable): What should a reviewer do with them? Recommend Close is wrong per definition and if Looks OK and Edit are correct, the whole flag was pointless.
- If questions exist, which are low quality but should not be voted to close: What should a reviewer do with them?
- If such questions do not exist: Why the low-quality flag? Questions can be flagged to close anyway.
Note that I am aware that there are other questions discussing the necessity of this flag, but they do not address the above paradox and were asked some time ago (so the system was not the same as it is today).