There could easily be confounders to that though. Like people who are wealthy might be able to delay satisfaction better than poor, because their needs are more satisfied.
Sounds more like the test is just testing for an adaptation that happens to be well suited to living in a upper-middle class to wealthy environment. If resources are scarce, the kid that takes what they can get now rather than trusting other people will do better in the long run.
Breaking the feedback loop usually involves doing something farsighted, risky, and irrational - for example, risking getting fired from your retail job by studying programming and applying to software engineering jobs in your downtime, or quitting your stable corporate job to found a startup.