The thing is, the concept of religion as a distinct, separate part of culture is basically a Western concept itself - and one that many scholars don't find to be very solid. Take Japan for example: Shintoism and Buddhism are very woven into the culture of modern Japan. Rituals, shrines, and other associated practices are quite prevalent and most of the population interacts with them on a regular basis. Yet your link lists Japan as being the second-least religious country, after China, which also has a number of beliefs that essentially qualify as 'religious' in nature.

https://en.wikipedia.org/wiki/Religion_in_Japan

In the Western world, the concept of humanist, egalitarian democracy is more-or-less an extension of certain Christian ethical beliefs that preceded it, so again, this definition of 'not-religious' is itself pretty problematic.