Why doesn't the majority US of A celebrate life?

You know, over the years I have became really cynical towards my own government, and I have every reason to. I love my country and plan on serving it once I graduate. I've always wondered why people get so upset about death, especially when they are religious (unlike me)... don't religious people feel they have a place in a Heaven for them? So many other cultures celebrate life, not mourn death like us... which makes people fall into depression and even suicide.. How can you be sad if say your parents died, but you honestly, have no clue what happens when you die. You could be a Jesus Loving Bible Craving Christian and you still have no clue what "death" is, we never will know... So why do people act like it's the end of the world when a close one dies? Is it out of involuntary selfishness that people act the way they do when someone close to them dies?