Wow, what clever marketing!
What parent would leave little PFB in a nappy they know is wet? They'll be changed straight away, so each nappy will become 'one wee use only', whereas previously, they might hold a couple or three wees before being changed.
Also, Pampers can now collect lots of juicy information about how often babies wee, so that they can guilt parents into ever more elaborately over-designed and expensive nappy purchases!