One would think that banks, who are the prime target for every person that "wants to hack", would be leading the way in terms of bug bounty programs and benefiting from smart people finding gaping holes in their systems.

This bank could have gotten into serious trouble with regulators if a bad actor exploited this bug and stole millions.

Don't expect them to adjust their behavior any time soon, but the "HN effect" might make them undo this action to avoid bad PR and make a few vague promises about "fixing the issue to avoid it happening in the future".