I think that the easy option has always been to believe, or say you believe, the same thing as those about you so that you fit in. I believe a lot (most) of religious observance is about fitting in and conforming. In some places it could be that being religious is the difficult option because those about you have no regard for religion and there is no advantage to be found in being religious.
Agnosticism is just not knowing and not accepting leaps of faith. Atheism is a firm fixed belief that there is no god and no afterlife. It is a leap of faith too. However it is easier to spell and sounds cooler so I reckon a lot of so-called atheists are really agnostic if you push them.
RE: What exactly does "Atheist" mean?
I would like to add two more excluded subjects4. Donkey Kong
5. Exclusion of interesting subjects