The 40 hour work week was the result of strikes and legal maneuvering by unions that led to labor protection laws in the early 1900s. Otherwise we would likely still be working those 80 hour weeks (alongside our kids).
It’s not necessary that the longer hours actually translate into productivity, just that the boss feels like it should.
And the fact that the strikes had a chance was largely due to improving conditions including, among other things, a working legal system that made it harder to flat out kill strikers.