I understand your point, but saying that Google has no incentive isn't accurate. There's always an incentive not to pay for bug reports, simply because it results in a short-term gain. Whether it's a good decision in the long run is another question.

It's more helpful to analyze the situation from a game-theoretic standpoint. Bug bounty programs are a typical example of a cooperative game. If someone reports a security issue, they start the game by cooperating. Google can then choose to cooperate by paying a bounty or they can defect by refusing a reward. Like in the classical prisoner's dilemma, both parties can typically maximize their rewards by choosing to cooperate.

My case is a bit special. While I don't know the exact reasons why Google chose not to reward me, it's possible that they thought I would continue to cooperate even after they defected. But like most rational players, I chose to stop cooperating, which ultimately leads to the worst possible outcome.