The Wikipedia article I got the info from basically says that mid-month was considered a good time for religious celebrations. With St. Nick being a literal religious entity, that’s probably why his “birthday” was put there.
The mid-month habit goes a lot further back than St. Nick too. For similar reasons to St. Nick’s birthday, Julius Caesar’s assassination is/was said to have been on that date (aka the ides of March). It might even have been. There’s no way to be sure.
The Wikipedia article I got the info from basically says that mid-month was considered a good time for religious celebrations. With St. Nick being a literal religious entity, that’s probably why his “birthday” was put there.
The mid-month habit goes a lot further back than St. Nick too. For similar reasons to St. Nick’s birthday, Julius Caesar’s assassination is/was said to have been on that date (aka the ides of March). It might even have been. There’s no way to be sure.