Does anybody know what has changed recently? Have they started using some kind of cheaper glue or less amounts of glue?
Most likely the ever-present pull to find an ever cheaper way to create the item.
The packaging for the product is a direct cost that is not explicitly what the customer is paying for. So saving a few pennies in an ever cheaper "zip-lock" style strip when multiplied by millions of items shipped amounts to a substantial cost savings.
And as most do not likely return the item for a broken resealable package, the makers receive little feedback as to the problems with their cost savings in this area.