I suspect that in an ideal world this rule would apply to everyone, but a lot of practical realities drive this decision making in my opinion.
There are some reasons to vindicate it though, as a tourist you mostly keep with your group, if you mingle it's mostly with other tourists I suspect, you don't have all your close friends and relatives or colleagues that you would really spend a lot of time with in variously intimate contact.
On the other hand, as you say they travel a lot more than locals in any given time period.
There are some reasons to vindicate it though, as a tourist you mostly keep with your group, if you mingle it's mostly with other tourists I suspect, you don't have all your close friends and relatives or colleagues that you would really spend a lot of time with in variously intimate contact.
On the other hand, as you say they travel a lot more than locals in any given time period.
Time will tell if this makes sense.