Supermarkets running these "Baby Events" are tricking parents who are trying to save money into believing they are getting great deals by buying disposable nappies at a discounted price when this is not true. It is also unfair to discount one type of nappy and not the other and thus ignoring the large community of cloth nappy customers.
Disposable nappies can take 300-500 years to decompose in a landfill and are known to have all sorts of nasty chemicals including Sodium Polyacrylate which in the 80's was banned from being used in Tampons as it was connected to Toxic Shock Syndrome. It has also been in the news over the last year where parents have had disposable nappies explode and the Sodium Polyacrylate crystals getting on their baby's skin and burning them.
Cloth nappies cost less in the long run and benefit our environment as well as local landfills. Many local councils have real nappy incentive schemes which include trial kits and/or cashback. With the help of supermarkets we can reduce the country's carbon footprint by simply offering cloth nappies in their stores and as part of any of their seasonal baby events.