Neither of these are the reason. I can explain>>115802845
I don't get foot fetishism w/r/t actual sex, but I can tell you why female feet are attractive. It's because bare feet feel somehow uniquely female.
I know that sounds stupid but hear me out. Most heterosexuals are attracted to things in the opposite sex that their own sex does not have. I remember hearing about this thread on tumblr full of girls who were obsessed with the way us guys take off our t-shirts. I hadn't noticed the difference myself, but apparently we take off our shirts in a very different way (pulling it over our heads instead of the cross-arm peeling it off), and some girls found that fascinating.
That's what this is about. Bare feet in and of themselves aren't feminine, but women seem to have this strange ability to go barefoot ANYWHERE. Inside, outside, on the grass, on the pavement... you name it. I myself am a huge tenderfoot, and could never go barefoot outside. But girls seem to do this all the time, and I find that hypnotizing.