I do hope this one is obvious, really obvious. In fact I’d be astonished if it was not, and yet so many of us still fall for it.
When somebody famous is engaged to push a specific product we all know in our heart of hearts that its just marketing hype, so why does it still happen? Well, basically because it works. The celebrity in question gets a wad of cash for their services, so they are quite happy to do or say whatever is required, and the advertiser reaps a jump in sales.