Hypothesis: Climate.

In colder climates, shoes accumulate snow, grit, wet and other nastiness. This remains attached to the shoe until the snow and ice melts.

In Alaska (and, from what I've seen, other northern locations), homes typically contain an Arctic Entry, a place to store shoes and jackets. It's typically an unheated space between the home and the outdoors.

In addition to serving as a storage space, it acts as an airlock, reducing heat loss from the home. Even older cabins sometimes contain Arctic entries, as frost and snow buildup on the outer door can keep it from shutting properly. Terry McFadden's Construction in Cold Climates talks about this feature of the Arctic entry.