It's why we are seeing the narrative written here of "controlling parents demanding their offspring stay put" yet ones who believe in moving away "gently suggesting something would be fun or have benefits" such as the poster who was advising the au pair.
I think the thing here is that you’re presenting these as two sides of the same coin, with an equally permanent impact, which is just not accurate. One is inherently permanent and exclusionary - don’t move away - while the other is potentially temporary, and more inclusive of ‘ultimately settle here’ - you should consider trying living in different places before deciding that this is where you want to spend your life.
The other issue here is motive and focal point. The ‘try living other places’ advice tends to focus on the person in question; it focuses on their long-term benefit and happiness. The ‘never leave’ advice, based on this thread, is at least in signifiant part focused on benefit to others rather than the individual - while the benefits to the individual have come across as secondary. Altruism vs (in part) self interest by the advice giver.
If local is the right place for them, when everything is weighed up, then that’s where they will probably end up, if you’ve given them confidence in themselves and the skills to make good decisions.
Ultimately, I ended up on the other side of the world; that was right for me even though the location wouldn’t be my first preference. I may not be here forever but it’s the right decision for now. My brothers are within two hours of my parents (which qualifies as ‘reasonably local’ for us). One is there for life, the other may move but has no current plans to.
However we are all happy, fulfilled in our reactionships and families and in our careers, and retain strong bonds with each other, in part because we were equipped and encouraged to choose the right paths for us. That’s the important thing.