It has a lot to do with the structure of society; family being the foundation for it. Parents pass all kinds of crap onto their descendants for generations, not just positive values, as Hollywood's half-hour family comedies would make us believe. For a person to get fully disassociated from that kind of baggage can be rather hard.
And +1 to everything roflsaurusrex said, any person can be non-religious, and still be a self-involved, close-minded twat full of personal defects, and viceversa.
Open minded people, with an appreciation for common sense, civility and reasoning are often the least unbearable fellow human beings. Whether they refuse to acknowledge the realities of death or not, that's rather unimportant in comparison.