Opening CW award availability means only those in WTP could UuA to CW, if WT/WTP is oversold and BA is trying to move passengers up through the cabins rather than op-up. And I would guess that very few people would check for UuA availability in the last few days of a flight. Also it would allow others to book the CW award seats who were not already booked in WT/WTP.

Easier for BA to offer a POUG/cash upgrade to all in WT and WTP, means it only is available to passengers in the oversold cabins.