ms101 as you suggest a very, very large number of seats to Tokyo were sold during the last sale which will naturally reduce the availability of 'cheaper' seats, including reward seats and upgrades. It would not surprise me if QR said stop for reward seats for some time so that the 'cheap' sale seats can be supplemented with more expensive seats in order to maintain some sort of profitability.
This is conjecture on my part and there may be other reasons.