One of the problems in complex societies is that specialization produces information asymmetries in the marketplace, and without reasonably efficient information exchange, markets don't work. Three thousand years ago, there just wasn't that much to know about fish or bronze, and even though the the fishmonger might know more than someone else about his product, the imbalance was far less than it is today. Today, someone's whole career (and a whole industry's R&D apparatus) is spent trying to get you (for example) to eat junk food, and you're spending your life trying to devote your attention to multiple things, so chances are more often than not they'll win. The same applies to any industry or profession you might name: finance, cars, medicine, ad infinitum.
It turns out junk food is an excellent example; here is an excellent piece showing how the food industry conceives and sells it.