Briefly, we as a society here in the U.S. no longer know what to do with our dead or how to grieve. We have sanitized the rituals of grief and the symbols of mortality into happy "celebrations of life" where we focus on the charming and cheery aspects of the dead and avoid the powerful and disturbing emotions of our own grief.
Mind you, it is all of a piece with our general unwillingness to confront the unpleasant or our powerful emotions generally, ceding that to the few who express rage on the political front. And, in perhaps the greatest irony, the rejection of traditional rituals of burial and mourning as stifling to the individual has become the means by which we are all repressed, homogenized and rendered suitable for polite company. It leaves us with a rich popular culture of people bemoaning the fact that they don't know how to feel.
I should add that there is nothing religious in the need to feel grief and mourn, although the long association of mourning with religious rituals for rather obvious reasons may account for why so many atheists of my acquaintance reject the idea of mourning rituals or other acknowledgments of grief -- either in their own life or for those whom they will leave behind when they die.