I’m not sure dude has the right answers here, he leaves out some glaring ones. Like, it protects the lower walls/ windows from rain and therefore decomposing. It provides rain proof space for people. You can throw things out the window like urine and not get it on your own house. Also, many buildings were built over time and the following build outs might have had more money to throw at it since the foundation was already done. there’s more, but until a proper architecture historian can weigh in he’s just throwing darts.