EvolutionThere is actually a scientific reason that "healthy" foods are less flavorful in general. Back during our hunter-gatherer days, food was much more scarce than it is today, and so food that was high in fat and sugar (and thus loaded with energy) would be more sought out and thus more pleasing to the taste buds. Salt has been prized for centuries (remember the Bible quote "you are the salt of the earth"?), as it can be used to cure and preserve meat for long journeys, not to mention its role as an important electrolyte. Unfortunately, like the appendix, this taste for sweet and fatty foods still lives on in our genetic structure. Couple that with our less active lifestyle brought on by technological advances in agriculture, we end up consuming more energy and burning less. Thus, foods lower in fat, salt, sugar and calories are dubbed more "healthy" than our more decadent choices.
MythSometimes, though, people are simply wrong. For example, cod liver oil is incredibly foul and really not all that good for you. (It is, in fact, somewhat toxic if you eat too much.) You can get the vitamins in it without having to choke down the traditional liquid form. However, the idea that anything that bad must be good for you is, for some people, really potent, meaning utter crap (like some herbal 'medicine') can endure long after we've either discovered an easier way of doing the same thing, or found that it wasn't worth doing in the first place.