The be vendors that offer the buttons for their products are probably financing the whole thing. They'll also be the ones paying for the buttons, as opposed to customers. Imagine how great it would be for a paper towel company to make buying its towels a single button press (with high coolness factor) whereas any other brand would require a trip to the store, or at least 2 minutes to order on amazon.

They could just automatically include the device in some shipments.

I think it's likely they are partnering with P&G at least on promoting this.