Could it be that P&O are attempting to maximise their profits which is their right I suppose. Bar prices are creeping up, spirits have been withdrawn from being able to bring on board, your supposed to hand over any alcohol bought in port. I wouldn't be surprised if next it'll be alcohol must be carried in your hand luggage on embarkation to stop doubling up in suitcase's then they could withdraw being able to buy spirits to consume in your cabin. All this then leaves guests with no choice but to buy from the bar or purchase a drinks package.
Now they're attracting a younger demographic and bookings are doing well they probably think they can push all this through without much fuss.
Sorry it's all a bit negative but .......