Shoes off makes sense if you have carpet as a floor covering.
I used to watch where I step in Russia. You walk and you watch each one of your steps. Because there is **** on the side walk. People walk their dogs there. People spit. You can step into some **** if you don't watch where you are stepping. You walk one way to the store, while watching the ground, and then 20 minutes later you coming back you still watch your step, because in that 20 minutes there could be some kind of new **** there.
In United States it's also somewhat similar, but not anywhere close. You still watch where you step because people here walk their dogs. But, difference is that people pick up their dog ****. Still, residue of some **** is still there. You better watch your step.
Frankly, you hardly ever walk in the U.S., you step out, sit inside your car and drive. Near the store people don't walk dogs. Near you job people usually don't walk dogs. So it's clean and you can actually walk into your house and not take your shoes off.