I've long wondered why people accept that having more life automatically makes it more meaningful. As a thought experiment I imagine this:

'A person lives a normal life and dies. In death they enter Heaven and are happy. They exist in Heaven for a countless time, billions of years, perhaps trillions. One moment God decides enough has been and declares that soon all existence will be gone. The people look around and scream to each other, 'what, you mean it was all pointless?'.

I've never seen anyone actually discuss this. Perhaps I've just not seen people discussing it. Every religious person I've spoken to has just accepted it as a base part of their argument, without ever really assessing it or justifying it. We'd never accept in life that if a person lived to 40 instead of 30 they had more meaning or that their lives had more intrinsic meaning, as opposed to they just did more or had more impact. If a child dies at 5 years old we don't talk about them being meaningless or having no worth.

We would literally never do that.

However, something either in people's religions or perhaps something innate in us is making us say these types of things to ourselves, even when we would never do it to others.

My gut feeling on this is that really its just the emotion related to death / our own deaths. That thinking we exist forever calms that feeling and that is being labelled as 'meaning' or 'worth'.

But I suspect there isn't really anything much deeper to it than that, which is why even if God is real and heaven is real and we all went and existed for trillions of years I can imagine people saying exactly the same thing if they ever encountered information that Heaven itself was of a limited timespan, or that God was. They'd all be like 'Oh, so God and heaven and me and everything is all just pointless then'. As if only infinity will satiate their needs.