please forgive the off topic,
I've wondered this too. I read that introverts or shy people end to look down a lot and some times is the thing they see most of in extreme cases.
I guess it's also an intimen thing. Out of most places on your body besides your yambag, people in most cases arnt seeing or touching your feet. or maybe its a modern thing. I imagine people 200 years ago had very rough feet from shitty or no shoes.
For some people it's a continuation of the leg, legs are sexy you know so you got me.