Redemption space does indeed appear to be zeroed out for the dates in question. WT+ is a popular cabin and the dates you've picked are covering the winter holidays so its not inconceivable to consider the redemption limit has been reached for these dates. I'm not certain using Avios to pay for this route /class represents great value anyway. Taxes and fees are still payable and would represent a considerable cash element on top of your use of Avios. If you're happy with the cash fare you've seen, I would purchase that.
If booked on ba.com (as opposed to aa.com) you can then see whether award space opens up for Club World (Business) and use your Avios to upgrade. The value aspect of what you're getting v the number of Avios required is also likely to be higher.