The last time a civilization had a purpose was Egypt, who wanted to figure out the secret of immortality.
Every ""civilization"" since then has merely been marking time. Exiting for the sake of existing, or because suicide is scary.
[Immortality] is probably a fairly dumb purpose, but it at least manages to be something you can either succeed or fail at. All post-Egypt ""civilization"" has been not even wrong. Can't succeed because it can't fail.