BIAHI:
Yes, I think in some cases younger people looking for adventure go to where ‘the need is greater’.
In other cases it is older people going to more attractive places - maybe not necessarily where the need is greater. Maybe these Witnesses are fed up with the daily grind back in the states. The ‘new system’ is delaying so they want to experience ‘paradise-like’ conditions now. What also needs to be taken into account is political instability around the world and how sometimes desirable places turn into something not-so-nice and the JWs need to move elsewhere!
Also, the problem is that some JWs weren’t exactly retirement age and not yet eligible for SS (even if they paid enough into it) when they went overseas! Maybe they had a stash of money and wanted to try it and hoped maybe the ‘new system’ would be here before the money started to dry up. So, now they are over sixty and have to deal with this!