Why are so many Swedes Atheists?
We learn at very early age to think critically, to use logic and reasoning. And have for a very long time. And because of this we are more liberal in nature and generation after generation grows up with religion on the side, not in it. You are always agnostic first, then you can choose, religion or atheism.
Here the government fear the people, not the other way around.
Religion is never a factor in any way when you grow up here. In school we go to church to learn about it, we are not forced to believe it; it is like going to a museum.
We celebrate religious happenings because of tradition, not faith.
When your start your life like this, and you have a choice, you choose the one that feels right for you. You have years in schools studying all the major religions, you know a little from all of them... then when the day comes most people choose atheism, for obvious reasons.
You can go much deeper than this, but this is a summary for how I see and experience it in my country.