Having started walking around the office where I work shoeless, I have noticed my socks get incredibly dirty.
The floor is not clean at all. Where does this dirt come from? People's shoes of course.
Readers, if you take your shoes off, but your guests keep their shoes on, you may find that your socks will get dirty. Shoes really do bring in dirt. The only way to keep the floor clean is shoes-off for all; no exceptions for the able-bodied.