It's probably because NW hasn't paid the lounge fee charged by Changi Airport. NW has been lack behind in paying their bills.

We as a crew members also suffered with hotel bills not being paid by NW, and in return we were not picked up at the airport (i.e. MCO, etc) as scheduled. They tend to pick up crew in a bunch (making the earliest group in the batch of flights to wait for the last flight to arrive). Also it's been known that hotels have been making crew members wait for their rooms to be available even though check in time was past after the hotel's official check-in time.

Welcome to Ch. 11 !!