They kinda weren’t, there were so many feast/ saint’s days, and the Chores had to be done anyway, that the idea of an actual rest day was unusual in Europe.
Discussion
but the law was originally built around a religious practice (altho, a lot of farmers would go ahead an milk the cow).
I pulled up a encyclopedia to take a gander (been quite a while since I read anything about labor history). Looks like it varied across the world, the Swiss getting there first, but mostly laws followed by enforcement around late 19th to the 1940’s.
All I know is workers in the US don’t get enough time off.