Foot or Feet?

For reasons unbeknownst to me I started wondering why athlete's foot was named for a singular foot instead of the more likely athlete's feet? I have never had the fungus but it seems that if you had it on one foot chances are you would have it on both feet,so what is the story on that? As often happens my mind was off to the races...most people will tell you their minds wander,not so with my mind. My mind sets out at warp speed building freeways along the way complete with workers leaning on shovels,the problem is directing it and I've yet to master that feat ( yet another feet,or feat to deal with!). I decided I would ask a knowledgeable friend who is used to my scattered, esoteric questions if she had any ideas about this misnomer,she did not and an internet search yielded zip. I thought it would be best if I didn't get carried away with pursuing it further...then this same friend mentioned that rental bowling shoes used to come with warnings about athlete's foot which in turn made me think of my youth when you had to either have socks or used a footie/peds (supplied by the store) to try on shoes at the store,which was also an effort to prevent the dreaded fungus. Now comes your part my faithful readers! I remember them handing you or your mother (or parent) a footie so your foot would be protected from whatever might be lurking in the brand new,but maybe contaminated shoe,but my recollection tells me that once you were done with the footie it was returned to the box or sometimes a jar it had just been removed from so it had served no purpose whatsoever since it could have already been used by a person with the fungus other than perhaps passing the fungus along to your previously uninfected foot. So the question is am I remembering this wrong? Did they actually throw them away after every use?  Of course in those days no one worn bike helmets or had seat belts either and most of us are still alive to talk about it!