Betty - I'm nearly as old as your mum so have a similar point of view.
To you daughters, talking about death is, hopefully, about something far away.
To us, it's something more familiar, often thought about. just around the corner. We're not here forever.
Thank God I still have a husband and we often talk about it. He always says we need to go together. So hoping he's not planning a joint car crash.
But I know our oldest daughter, who we see most of, feels the same as you older folk. I daren't tell her how we feel about death, she would crack up.
Perhaps that's the difference with your mother Betty, she seems to have lost the social skill to imagine your feelings.