Because taste is largely based on smell. You don't need to know the exact nuances of the taste of shit to know how horrible it would in fact taste.
Meh, sort of. Slightly different types of chemosenory reception though, which is why things taste and smell different. One of the reasons things can smell hideous but taste delicious, and visa versa. Of course one can add on top of that various genetic factors that can make the same smell/taste appealing or hideous, and on top of that additional factors that can make certain elements of taste or smell entirely absent or active.
Cheese is one such example already noted. Cumin, cilantro, and a lot of other spices are in that category too. Broccoli, coffee, etc.
Maybe you like the smell of almonds? Well that's all fine and dandy, but certain bacteria that can infect open wounds cause similar smells; doesn't mean it would taste good.
So... something I love, Chemosensory reception!
And tetrachromacy. How senses work (and could work) is utterly fascinating.
Many animals practice coprophagia.
Guinea pigs too. Usually, however, in species that do this as part of normal behavior the feces that is ingested is actually of a different consistency and format from normal fecal matter. In most instances I am aware of, this is more of to ensure the continuation of necessary intestinal bacteria. Sort of like a human eating yogurt after taking antibiotics (though, as fun trivia, there is some hint that the appendix might have served a similar purpose in ancient times).
Dogs have been known to particularly love cat poo, regardless of the health of the dog, which may stem from different digestion systems extracting different nutrients. Cats being stricter carnivores than dogs might indeed be incapable of digesting (or sufficiently digesting) any plant matter contained in their food.
Whatever it is, cat poo is like dog candy.
And on that note, here, have a related web comic:
http://www.itswalky.com/d/20090117.html