Why do people who strongly believe in a good afterlife get sad when someone dies?

I’ll be honest I’m going to mostly be going off of the Christian afterlife because that’s the one I’m most familiar with.

Here’s a scenario: Person who believes in an afterlife is given the news that their grandma dies. She didn’t suffer in her death, she had the same beliefs as them, and they have no reason to believe she wouldn’t go to the “good” place. Why do they get sad? I get if they’re sad because they won’t see her for a while, but I don’t really understand why they go into deep grieving. Aren’t they going to see her again, and isn’t she in a better place?

I got sad when my grandfather died because he’s gone, and I’m never going to see him again. That’s what I believe happens when you die. I’m sorry if this sounds really unempathetic or ignorant of different beliefs, but I don’t really get the point of believing in an afterlife if even a peaceful death is very sad.

I understand if the answer is it’s just human nature.