I can understand eating ass, because I've done it before, never understood foot fetishes
it's partially a pheromone-scent thing
for person who likes women's feet, there's an ability to smell the post-puberty-foot-pheromone
when you wash off all the sweat and dirt and foot fungus and rinse away all the soap
there's a pheromone scent where a woman's feet smell different than a guy's feet
the female-version of the post-puberty-gender-identifying-foot pheromone is a scent that makes a lot of straight guys get a hard-on
(it's kinda the same as the scent being inhaled when someone loves getting golden showers)
there's also
the foots shape
most foot-fetish guys want the feet to be "feminine shaped"
long, slender, high-arch (the bottom being arched, where if she's walking bare-foot, there's a section of her foot that won't ever touch the ground)
most foot-job videos the feet are all the same shape (being the shape that's a good-shape for giving foot-jobs)
when it comes to the guys that actually prefer a foot-job over a hand job, the soles of the feet are a noticeably different texture than the rest of the body (a better texture than the rest of the body if you've removed all the walking callouses) and with the walking callouses removed, when a woman's callous-free sole touches my skin i (and prolly a lot of other guys as well) can actually feel the foot-pheromone moving from the soles of her feet into my skin (not just the woman's soles on my dick or balls, but the sole of a female's feet on any part of my skin, the skin-to-skin contact always feels amazing when the other person's skin is the callous-free sole of a female's feet)
the foot licking and toe-sucking is just the guy's tongue tasting the female-foot-pheromone