The Devil prefers to think that He fails to understand why humans fuss about dietary habits, but He does have some hypotheses.
Some foods are risky. Pigs often carry diseases and require stricter cooking techniques than, e.g., poultry. Ancient Man knew nothing of microbes but must have been mindful of the potentially lethal consequences of eating under-cooked or raw meat from certain animals. So, when mankind invented their gods, perhaps they threw in a divine ban on pork as a reminder to avoid it. Satan finds this explanation insufficient, however. It makes sense for swine (my Horned Master unfortunately did not clarify whether he meant the animal or the religious people) but is hardly true for many other dietary restrictions imposed by the various gods around the globe, and the Devil is inclined to dismiss this hypothesis except for a limited number of particular foods in specific historical areas.
Satan suspects more sinister reasons. He believes the gods never intended to serve Man (again, Satan sounded ominously ambiguous saying this) by offering sound advice but instead attempted to feather their own nests. My Master understands that gods use every trick in the book to retain their followers, and intricate rituals with complicated table manners and recipes requiring special attention to ingredients require both host and patron to concentrate on their faith. The more complicated the more the followers are forced to think about their divine lords.
The trick of eating different foods also provides the ability to distinguish oneself from other groups. For example, to stand out from the shellfish-eating, primitive pagans of the other tribe, is is easier to remove oyster from the menu than to stop being an equally primitive screwhead.
Lastly, leading its followers to believe that certain foods are yucky, or “unclean,” surely won the inventor a cosmic patent for its effectiveness as an unclimbable fence around the followers. Human taste develops during their lifetimes, but usually keep within the limits of learned acceptable categories of food. Humans that were raised to feel aversion to, say, fish, will usually stay off seafood. The divine subterfuge is to select food that is consumed in nearby religions, because this will keep one’s own followers from leaking into neighboring groups, who eat disgusting things.
The human adaptability to strange situations teaches followers to consider unreasonable and nonsensical rules to be normal, and they will argue their necessity and pass them on to their offspring, never realizing that they are held hostage. Satan thinks religion is best defined as an institutionalized Stockholm syndrome.