SPG probably didn't want to single out Southwest as the one partner for whom SPG points only yielded 0.8 partner points. Southwest certainly didn't want to single out SPG for special points pricing to prevent a cost increase for SPG. It was better for both companies simply to eliminate the transfer option. Customers? Who cares?
Single out???
They could have just made the transfer ratio 0.5 (ie, 2:1), in which case they'd have the company of UA (and I tnink some others too?)!
(Ie, there's major precedent at SPG for some arilines transferring at less than 1:1. WN would have hardly been the first.)