In your childhood you learn about life and how to go about it, in a language that had its own syntax and vocabulary. When you immigrate the language of life changes on you. Most  people either live in the same place all their lives or move a few times; and like in plants, early clean grafts can usually adapt and survive simply. But too many changes and too much going back forth, are harder to learn to navigate. Gradually your ability the learn to understand - and moreover learn to like - a new place and its customs - runs out. In parallel, the amount of life that stretches out in front of you reduces - perhaps that also impacts your motivation. As you get older, and your story gets more complex, your ability to share it with others, or make genuine friends, reduces. So on top of everything else, you become lonely too