If life is so terrible, why don't the vast majority of people kill themselves? Of course there are sucidal people, but given that being suicidal is relatively r

If life is so terrible, why don't the vast majority of people kill themselves? Of course there are sucidal people, but given that being suicidal is relatively rare, and is often the result of issue like depression rather than rationally thinking it would be better to be dead, it seems like most people are happy to have been born. And if it is immortal to have children, doesn't than mean it is completely moral to kill children painlessly, since it would be better for them if they had not been born? Maybe I don't understand the position fully though.