Why are parents or aspiring parents scared of nothing living on after them once they're gone?

I get that people have a variety of reasons to become parents

But the biological reason is to avoid extinction

Why tho?

Why are humans scared of becoming extinct?

If we're extinct that means we all die. And if we all die then that means it's peaceful nothingness

And plus, parents are never gonna know if their child actually passes on or continues living because they themselves will die on by old age age

That's why I don't understand legacies that much.

Especially when expecting an autonomous human being to keep the repetitive tradition going is unrealistic