It’s because it won’t be upgrading into R space but instead hidden space the algorithm for which takes into account the price of the ticket. With the higher fare that you would be paying for PY flex vs lattitude here revenue management thinks it’s worthwhile for them to give you an instant upgrade if you buy PY flex but not if you only buy latitude. If you were to find R space through expert flyer both would be upgradable when there isn’t R space they both could be, neither could be or somewhere in between it’s all up to the black box that is revenue management.