Death and dying are a part of life but for most people those words elicit discomfort. No one likes to add to the hurt and pain of someone by being too direct.
How often have you used - or heard someone say "passed or passed away?"
Resting in peace or in a better place?
Was called home?
Kicked the bucket?
Gave up the ghost?
The list goes on as often characterized by a culture, location, or the individual. And how comfortable you as the speaker are with your feelings about death will temper your comments. Is it easier for you to say that you are sorry that your Dad "didn't make it" instead of coming out and saying "he died?"