If you lived on forever, who knows what the future may bring? If some freak asteroid hit earth and killed everyone, Than anything could happen to you! After all, Your Immortal. You cannot die.
You still want to get away from threats, Even if you immortal.
Speaking of the future, What if humans had totally transformed? What if they looked different from the past? You’d still be alive, But you’d look so paranormal to them. The future humans could look like anything. It just depends on how the future plays out.
In Greek stories, A foolish individual may be put in forever pain due to what they might have done. Now Imagine that with you, in a situation where you cannot get out and you stay in forever pain. Harsh, Right?
For instance, What about a grinder? Forever going up and down, Crushing you.