I have a hypothesis.
Over the years, I've seen a steady increase in the number of posts of people saying they like to eat ass. As a person who finds kissing someone on the lips more intimate than penetrative sex, the idea of doing so to someone's asshole was always repulsive to me and so the frequency at which I saw these posts about tossing salads always puzzled me when I saw them.
Well, are you familiar with pica?
It's when people (usually young children) have a compulsion to eat something that isn't "food". The most common one is children eating rocks and sand. The interpretation I've always found most realistic is that they were lacking in some sort of mineral found in it or some sort of microbe that their digestive systems need.
Could it be that they are subconsciously associating the gut biome of people they are attracted to with good health, and so seek it out?