I cannot comment knowledgeably on the cultural reasons why people designed and purchased so ornate machines, but I can tell that part of the reason can most probably be found in the manufacturing method. Old cash registers had at least partially cast enclosures, and it's quite cheap to produce ornate decorations in metal casts - you basically only have to invest a little bit more when making the tooling for the mold.

When enclosures began to be made from sheet metal, adding similar decoration became suddenly a significant extra expense.