Because any payoff would be worth the effort. It's the same as people spamming bug bounty programs by using publicly available scanning tools. All it takes is

Because any payoff would be worth the effort. It's the same as people spamming bug bounty programs by using publicly available scanning tools. All it takes is one success anywhere for people to keep trying to spam every possible endpoint. It's why people stand at street corners with signs. It's also why people gamble at casinos. It's why loot boxes sell so well. Humans can not resist the urge to continuously throw effort at things with rare, intermittent rewards. Cost/reward is not taken into account, only the reward. Sadly, belief in a reward is enough to trigger this. There never needs to be any actual reward.