Why is the guy in the ancient inn called Xiao er? Why not call it Xiao Wu?

"Shop assistant" refers to the waiters in ancient restaurants and hotels, so why are they called "shop assistants"?

In the old society, ordinary people living at the bottom of society generally had no names. Only when you go to school can you have a scientific name, and once you become an official, you will have an official name. However, only a few ordinary people can go to school or be officials, and most people don't have this opportunity. So their names are mostly called by generations or the age of their parents. For example, in the Ming Dynasty, Zhu Yuanzhang's great-grandfather was called May 4th Movement, his second brother was called Liu Chong, his third brother was called Chongqi, and he himself was called Chongba. The waiters in ancient hotels or inns were obviously ordinary people, so people should also give them a digital symbol to address them. The boss in charge is of course the "shop owner", and these waiters are also called "shop assistants" accordingly.