Of all the people I know who have done this, the expectation always seems to be “ oh well people will come and visit.”
Even though you’re family, you’re not necessarily the big draw you think you are. The novelty wears off after a few times and as PPs have noted, adult children grow up, have constraints on their own time, have children, want holidays that aren’t just going to see you etc.
I have a few friends who have done this and our friendship has dwindled because no, I don’t want to spend a week of my precious annual leave going to see them when previously we would have caught up a couple of times a month in person, thank you.
The older couples I know who retired abroad and left their children in the UK have either come back because of health issues or to become more involved with their grandchildren as it just wasn’t satisfactory to see them at best twice a year, money permitting.
All of them had passable French/Spanish/Italian but even they said that navigating bureaucracy was a nightmare, particularly in France, it seems.
I see my own parents every couple of weeks and they only live about 50 miles away. I fully expect to want to be available as and when they need more support from me (I’m an only child) so when we took the decision to move house, I purposely didn’t want to make things more complicated than they needed to be by putting an unnecessary distance between us. What a 21 year old says now about not minding, and what they might think in 15 years time will be very different when they are staring down the barrel of navigating your health care.