What are the reasons that soap has so different smell and flavour?
It is possible for a substance to not smell very much, but to taste very strongly - chili peppers are a great example. They (in my experience) have a rather weak spicy odor, but the taste is much much more intense. In the case of soaps, very small amounts of essential oils are used to give soaps their odors. You may be able to slightly taste them were you to eat some of the soap (definitely NOT recommended!), but the major taste you'd experience is the actual soap - the saponified surfactants that do the cleaning.