In short when one learns of another's condition it touches their mortality. How they deal with that information gives information to both their attitude and willingness to understand the condition.
I understood this well before I was DX'ed with D.
My mother, before she passed, spent 4 years in a Alzheimer's unit and I had to care for her. It was absolutely appalling how many of her fellow residents never even got a visit from a family member. They didn't want anything to do with it.
I remember talking to a daughter of one of the residents and how she told me all her siblings refused to visit their mother because of her Alzheimer's. Out of 4 siblings she was the only one that cared for her mom. Point being even within families this occurs.
Yes as you say they have to work through it, but some never do....