It is about probabilities, more take-offs are on dry than wet,
Which to me seems the problem with the latest (EASA?) missives about using wet performance on a damp runway, we are using wet figures far more often than we used to. In the "old days" wet meant wet, or "would you get a wet arse if you sat down on it?" as an old skipper I flew with used to say. Is the braking action really that much worse on a runway that is slightly discoloured (the definition of damp) than a dry runway that we need to use wet performance?