I think the difference the author fails to take into account is (a) religious beliefs, (b) purchasing power, (c) economic class.

Respectively,

(a) Religious beliefs differ between countries and if someone believes that "sharing" is better than "self-interest" that will effect the outcome of this "game." This could help to explain why this country is relatively poor.

(b) $100 in the U.S. is equivalent to significantly more in this country...

(c) If everyone is very poor and you are very poor you're in the same boat, if your neighbors would be angry that you took $100 and left them out to dry this could be pretty bad for you. Even if this is not the case, you feel bound to these people and you likely don't want to "screw them over"