For me the shoes thing isn’t about dirt. It’s about public bathrooms. If a shoe has stepped in a public bathroom. Especially those in bars or gas stations I don’t want that shit (literally) being spread al over my house.
My dogs step in their own shit sometimes. They're idiots, but I still generally wouldn't assume a dog hasn't stepped on a surface worse than a public bathroom.
In New York a lot of dogs wear shoes when they’re out in walks, which I assume are taken off when they go back home.