Hmm, I can see the point ... on the other hand, having a sudsing medium can be a good way of moving a substance over a tricky surface, like for instance medicated shampoo. It's a lot harder to get something in and around an area with a lot of intricacies (like a head full of hair, or all the nooks and crannies in one's teeth) without foam to serve as a vehicle.

That said, they don't need to put it in everything ...