Why do people feel that marriage and children is what completes a persons life???

I personally dont believe in marriage, im not excited with the idea of children. What I think will complete me as a person is have a job I love doing and live in a small apartment with lots of comics,books and a cat. But people still insist that I will change my mind and at some point I will , for sure , want to get married and have children..

Because I will be a failure if I end up “alone”…