Because unless you're talking about a single molecule of water, water is always covered in more water.
But that's beside the point.
Practically speaking, a person considers something "wet" if contacting it will make them wet. If a person contacts water, they will become wet. It's not about the technical definition of "wet" - it's about the practical implication of the word and the effect it has on people and things around it.
Just like how even if Google does not technically have a monopoly, their influence over the market is monopolistic in practice and has the same adverse effects as a monopoly.
