Like 1% of the population is wired slightly different where they find feet attractive, like most are with tits and ass.
As someone with the fetish, it's more weird people aren't into feet at all. Women paint their nails, get pedicures, often show their feet off in public with open-toed shoes -- to me it makes sense a woman's petite feet are a sign of good health/cleanliness/attraction.
That said, I still find most women's feet ugly. But the attractive ones with nice feet are a big turn on. Not entirely sure why some of us are wired differently, but many of us are. And many other kinks out there make a whole lot less sense when it comes to reproduction (i.e. homosexuality, golden showers, furries, etc).