Well, its probably different for every individual, but its no different than someone liking lips, legs or even titties or asses. There is a certain appeal to feet to me because I know most people dont give a damn about them and therefore make no concerted effort to properly groom them. So, a woman that takes that extra time to do so gets extra points with me. They look so sexy in heels and what not, but thats just my opinion.
Honestly I cant call it. as a young kid i always like girls legs in stockings. At some point that morphed into liking feet and toes. Then once i got a girlfriend and smelled her feet and sucked her toes I was hooked!!!!!!