Having a routine that makes you happy is important and not bad advice!
But sometimes, at least for me, I kind of exhaust my options for happiness in a given environment. Eg maybe I've already gotten a job with the best employer in a given location and can't climb any higher professionally, friends have moved away or started a family or whatever, hobbies and activities that used to be novel and fun have become repetitive and dull, I've mastered the local language I wanted to learn etc etc.
That feeling, combined with a basically infinite and always in flux list of places and things I want to experience before my time is up, makes switching my environment up very powerful and enjoyable for me.
Happily admit there's downsides to not "settling down" too and it's not for everyone. But I think most people would benefit from fundamentally switching up their environment at least a few times in their life. If it turns out you were happier where you started you can always go back. But you'll never know other places if you don't give them a shot.
2) happiness. In my understanding it’s a decision about how to view life in general, which couples to endocrine system responses
3) the opportunities and relative merits of different places. I heard said that XYZ is a good/bad place to do PFQ activity