Gallup polling says 1% of people in the US didn't believe in god in 1967, 17% in 2022. Of those 17% i'd imagine many believed at some point (or went to church/temple/...), these people don't really behave like a 'pure' atheist would. They're very much still influenced by the religious ideas they grew up in. So yes it's a rather new thing if you're thinking about society.