Not so much due to concern about the welfare of the affected JWs. Rather, it was the loss of control. If a New Orleans JW was relocated to Texas, what meetings would he attend? How would the elders spy on, er, shepherd, them? What if a relocated JW discovers "hey, these 'worldly charities' are not foaming-at-the-mouth devil worshippers"? What if he needs to go to a hospital - how would the local HLC be there to enforce the blood prohibition? What if a few dozen, or a few hundred, fence-sitting JWs used this an opportunity to "fade" from the organization?
FFGhost for the win!
If you had to boil the Watchtower down to one, single point it would be this - control.
FFGhost is correct in his belief that if a large area was affected by a catastrophe the only way the Watchtower could continue to control Witnesses living there is to make sure they had provisions to stick together and hold out. Witnesses being forced to intermingle with non-Witnesses provides an opportunity for ultimate truth - personal experience.
Witnesses would come to see non-Witnesses are real people. The Watchtower narrative would fade away. This would cause Witnesses to begin to see things as they are, not as they are told, and begin to ask questions.
Stephanelaliberte - It could be World War III, the Zombie Apocalypse, and Sharknado 5: Global Swarming outside and the Watchtower would refuse to allow your residence as a safe shelter for the congregation. It would risk exposing those Witnesses to the truth about the Truth.