-The poster hadn't considered that argument
-The poster doesn't want to have kids
-The poster will have a finite number of descendants
-The poster's concern for the standard of living of his distant descendants diminish according to distance (for instance, he probably cares a great deal for his children and a similar amount for his grandchildren, but by the time you're talking great-great-grandchildren his empathy has diminished significantly)
-The poster's descendants will not want share his fondness for the Maldives
-The poster's descendants will move away from the Maldives for other reasons
I'm sure you can think of a half dozen other alternatives if you think for a minute.
2. Same as barren.
3. Impossible to know, and under any plausible reckoning of improvement, insufficient to make activation costs predominate.
4. Same as doesn't care.
5. Unlikely; goes against millennia of empirical evidence that people love where they live (nowadays we call that 'patriotism')
6. A fully general counterargument (http://wiki.lesswrong.com/wiki/Fully_general_counterargument). You can use that to argue against anything: 'You should move away from North Korea', 'Why, my descendants might move away into it for other reasons!'; 'You shouldn't move away from North Korea, then', 'Why, my descendants might then move away elsewhere for other reasons!'
5 (his children may not be fond of the Maldives): You just argued that children are likely to have a fondness for wherever they are born. If true, this invalidates the argument for moving at all: whether his descendants love the Maldives or America will make for no gain at all.
6. (children may move away from Maldives): Actually, given the limited economic and educational opportunities of the Maldives, there's likely to be a fairly high probability of one's children moving. Once we use this probability to work out an EV for "number of descendants resident in the Maldives", or even apply the probability recursively to work out a proportion of descendants resident in the Maldives over an infinite number of generations, your infinity argument is pretty well refuted.
What makes you think people consciously consider it? Most of them just say "I don't feel like moving", or "I'm too lazy". Also, you missed the point of the "fully general counterargument". The point is that if your descendants find it better to be somewhere else later - well, they're fully capable of moving themselves.
You're right that it would increase their incomes. But standard of living is much more than income...