Yes, I do realize the JWs can isolate themselves in ways other than physically. However, when somebody is geographically isolated, and especially when they leave the country, they are totally vulnerable and cannot receive help or if it does come it may be too late such as what happened with the People's Temple. I am only imagining how much worse it would be if JWs were geographically isolated like those other groups. If you think they are bad now, just imagine the other scenario!
When a group is still technically part of society and "in the neighborhood" they are more subject to being prosecuted or have neighbors and people in the community complain that something wrong or odd is going on, etc. Again, this help may be too little too late, but a heck of a lot better than if the group is out in the desert somewhere or took off to foreign soil where they are more out of the reach of any authorities and more likely to be headed by an extremist or dangerous personality(ies).