We have an evolutionary aversion to situations and things that may lead to our deaths. Staying alive is a “terminal goal” for most humans, not an instrumental goal (with the exception of people who seek to commit suicide as you point out, but evolution doesn’t need a 100% success rate). The argument that self preservation is a convergent instrumental goal is a more general statement about goal-seeking agents.

Think of a person with no attachment to his life. He’s not suffering in the way suicidal people are, he’s just indifferent about whether or not he keeps living. But he has a child who he is committed to giving the best life possible. He will act in a way as though he wants to preserve his life. He doesn’t really, but in order to accomplish the goal of giving his child a good life he needs to stay alive.