I agree. BA just hasn't released the seats yet. I can find decent availability in CW on other routes just a couple of months from now so I suspect seats haven't been released.

As an illustration, although for a different class of travel and different dates, I've been monitoring BA's website for WT+ availability from LHR to BWI for 9/2. A couple of weeks ago there were 8 seats available, a week ago 4 seats available, and three days ago, 0 seats available. Yesterday, there were 3 seats available and today, 5. I doubt that 8 people booked seats on this flight in the past two weeks and I doubt that 5 cancellations occurred in the past 2 days. I'm guessing that BA's revenue management software may have withdrawn and added availability as anticipated capacity went up and went back down.

The lesson, as with booking all award travel nowadays, is not to hesitate if you see seats available; they may not be there in a day or two. But may be in a week or two. As BA says, "Book now to avoid disappointment."