I always wondered if these geniuses think it’s such a great place why don’t they just take a long walk off a short pier now

I'm gonna use Ken Hamm's line, where you there?? No, well how do you know???
They say that because their giant book of fables tells them that they're either in heaven or hell. I understand your frustration. I can show you where my daddy's been for the last 19 years, and it's not heaven or hell.

And they know that how?

They are just trying to comfort you and each other in the only way they know how. I never take offense when this happens.

Is it not a suitable distraction, even if untrue, from what is happening to your deceased friend now ? Worms, dehydration, decay etc

It's just a comforting ritual to them, like a little magic spell to buffer grief. I try to mentally translate it into 'they are no longer in pain'.
And sorry for your loss.

For my own sanity whenever I hear a response like that I don't think about the verbiage but go with the sentiment. Most if not all times it's meant as a comfort. When I view it that way the words don't mean anything.