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Fifty thousand years ago, the taste buds of Homo sapiens directed their bearers to the scarcest, most critical food resources—sugar and fat. Calories, in a word. Today, the context of a taste bud's function has changed, but the taste buds themselves have not. Calories, far from being scarce (in First World countries), are actively harmful. Micronutrients that were reliably abundant in leaves and nuts are absent from bread, but our taste buds don't complain. A scoop of ice cream is a superstimulus, containing more sugar, fat, and salt than anything in the ancestral environment.
No human being with the deliberate goal of maximizing their alleles' inclusive genetic fitness, would ever eat a cookie unless they were starving. But individual organisms are best thought of as adaptation-executers, not fitness-maximizers.
A toaster, though its designer intended it to make toast, does not bear within it the intelligence of the designer—it won't automatically redesign and reshape itself if you try to cram in an entire loaf of bread. A Phillips-head screwdriver won't reconform itself to a flat-head screw. We created these tools, but they exist independently of us, and they continue independently of us.
The atoms of a screwdriver don't have tiny little XML tags inside describing their "objective" purpose. The designer had something in mind, yes, but that's not the same as what happens in the real world. If you forgot that the designer is a separate entity from the designed thing, you might think, "The purpose of the screwdriver is to drive screws"—as though this were an explicit property of the screwdriver itself, rather than a property of the designer's state of mind. You might be surprised that the screwdriver didn't reconfigure itself to the flat-head screw, since, after all, the screwdriver's purpose is to turn screws.
