Stupid question: why are the Bond Street, Tabak and other shave soaps brands exclusively for shaving? I mean I used bars of Dove and Pre de provence in my life, but I don't think you can shave with those. So, what distinguishes a soap as one to shave with?

Thought I knew the answer, but after heading to a couple of nonshaving stores with soaps, I realized I had no clue, why a shaving soap was just that and a bath soap bar was not the same, or maybe it is?