The only clues I can offer is the process. That is a topic now and then at the forums while more often is receiving a lack of traffic symbol. I guess I would first have to ask the surrounding circumstances to fathom a guess. I presume you are talking about a 'New Hub'? and it was also not featured?
Who to bring it up to is an email to HP. They will want you to be as complete as possible with the description of the problem. Theother is to post at the Forums in the 'Improving Your Hub' section for others to review it. There are some astute reviewers with experience that share openly. Some not so much. One should expect criticism. However, an edit will send it through the eval process again. That is next . . .
A new Hub
With a new Hub it is read by readers at a service called MTurk owned/operated by Amazon. And, it is checked by bots with algorithms. A reader for MTurk is tested by HP somehow and evaluated again periodically for proficiency. They have guidelines to follow. Those can be found for both informational and creative articles at this link . . .
That also leads me to believe those two checks - bot & MTurk, determine the original score.
When a new Hub is published to see how many times it was read by MTurk you can see that at the My Account Page → Traffic Sources link above the listed Hubs. Once there look at the 'Domain'. Below are the domain sources.
It may be best to sort at domain since it is alpha. Look for 'mturk' and then glance at the 24hr, 7-days, and etc. If they have read anything recently you will see that indicated. With a new Hub you will see activity in the 24hr and 7-days.
The edited Hub I 'think' goes through that process again. Speculation is if a major edit or not. Perhaps with an edit checking the Traffic Source may offer a clue. I have not tried that myself.
Other cases for receiving a low quality symbol could be:
Unpublished and revitalized thus possibly MTurk
A Hub Reported by a reader as Low Quality and reviewed - MTurk? (See red report link at top right of Hub for possible reporting reasons)
Triggered by a bot review with an algorithm and sent to MTurk?
Other than that I am guessing as well as speculating . . .