It's not a ploy, it's a legal requirement.
"Most food packaging will have one or more of three date labels: best before, use by and display until. The 'use by' and 'best before' labels are required by law – Directive 2000/13/EC of the European Parliament, implemented in Britain by the Food Labelling Regulations 1996. The 'display until' label is added by retailers to help with stock control.
Best before
'Best before' dates relate to the quality of the food, its taste, texture, aroma and appearance. If food is stored according to package guidelines, it should be at its best up to and including the 'best before' date.
Food should be safe to eat after the 'best before' date, but it might not be at its best quality.
Retailers can sell food after its 'best before' date provided it still complies with the Food Safety Act 1990 and the General Food Regulations 2004. These make it illegal for someone to sell or supply food that does not meet food-safety requirements or that does not meet the consumer's quality expectations. It is illegal to sell or give away food after its 'best before' date if the food has deteriorated so much that it does not meet these expectations."