There are quite a few studies with the opposite conclusion where there is no change in behavior. One thing that could explain this is a push up to a higher tax bracket for participants vs the control group. A portion of their income falls into a higher marginal tax which is less of an incentive to work. This also does not report on expenses which also might drop. Instead of having to take high interest loans, that extra $12k can avoid cong to take pay day loans to make rent or not pay 15% on a car loan. So while working Indonesia may drop $500/yr, equivalent expenses likely dropped even more.