The difficulty of a problem scales in an adversarial environment.

Yes. But the problem is that Amazon themselves would be an adversary to the idea of putting in the required effort for no financial benefit to their business, not that they would be trying to stop other adversaries.

They have solved or attempted to solve plenty of problems just as hard as this one, even acknowledging that this is an adversarial environment. But they generally only choose to do so when the payoff to them is worth the effort. In other words, they can properly tackle it, but they wouldn’t want to.