I live in Canada where it does snow in the winter so you have water/salt concerns but even in the summer there is still the risk of dusty dirt coating the bottom of your shoes and other random things, like bugs you step on, gum, gasoline at the gas station, a muddy puddle, etc.

I travel a lot for work and I even take my shoes off before walking around in my hotel room 😂 just a culture thing I guess.