I vote for sold out of stock.
I used to watch the refurb store alot. There is never huge stock in there (at least where I am). It can empty out pretty quickly at times. And I think usually there is only 1 for each option in the list. If people were waiting to buy and didn't like the updates they would have pulled the trigger on a refurb fairly quickly. FYI they usually only update it once a day - midnight or 1am where I am depending on daylights saving time. It shows no stock for about half an hour at that time and then comes back up after 30mins or so.
Edit: Checking the refurb store now there are alot of 2016 13"s still, but the number of 15"s has gone down since yesterday.
I just checked as well, and inventory reflects what was there this morning: one 2015 15" and one 2015 13" Not sure where you're seeing "alot of 2016 13"s still" cause there's none. Zippo. Zero. Maybe you're in another country?