The act of vengeance demanded the expenditure of resources that may have been better employed in winning the game or in their next move in the game. So perhaps keeping that 5c gave them greater utility than spending it. Notice that the article only says “worse” and not “bad”.

As a general rule of thumb, I’ve heard that people hate losing something twice as much as they love winning the same thing. (Thaler and Sunstein for example, and it crops up in various other places). So perhaps the 5c they spent/lost simply had a greater negative emotional impact than if they’d not spent it, unless the 15c deducted from the free-rider were to be considered a gain?

Alternatively, perhaps the 5c expenditure would be seen as paying more towards the free-rider problem, on top of what they’d already been cheated out of. They said they’d feel better about the free-rider being punished, but it doesn’t appear to suggest that they were asked how they’d feel if the punishment would incur a further cost on the punisher.

Another possibility could be the immediacy of the feedback. It could be more about feeling worse after paying 5c in what is essentially a tax to pay for justice, and seeing what that tax is spent on. By associating cost with justice, it perhaps made it less desirable: whereas usually we wouldn’t necessarily consider the cost of taxes when being avenged.

I think of this in context of the Palestinian Arabs, who have spent the last 60 years sacrificing resources in futile pursuit of “revenge”. They refuse to move out of squalid camps into new housing because they might lose their “refugee” status which theoretically entitles them to “return” to pre-1948 homes (and throw those accursed Jews out).

Meanwhile, Vietnamese “boat people” who lost everything and wound up in Louisiana have built up thriving shrimp-boat operations.