I don't quite see how things like yoghurts, that have perhaps 2-4 weeks before the use by date, can run out. They're not something that has to be ditched that day if not used.

Is there a long game for reductions in food?
You get nothing on the plane so have to eat in the lounge.
More people eat in the lounge which puts more strain on the caterer's budget so they have to make cuts and reduce the quality of offerings.
More people dislike the lounge food and eat outside the lounges.
Less people using the lounges means BA doesn't need them as much or can reduce costs.