[filoleg]

Interesting observation.

When I lived in a city in the US that had regular snow and ice, floors inside of the buildings were never slushy/dirty, despite everyone wearing the same shoes inside and outside (businesses only, inside my house I always take them off no matter the time of the year).

However, back when I lived in Russia, we had to bring an indoor pair of shoes to get changed into, as everything would be covered in a layer of outside of dirt otherwise.

I honestly have no idea why that was happening, but I wanted to make a point that both you and OP can certainly be correct on that one at the same time.