Suppose that everyone has raised their house up on a pile of dirt. The rain comes down. It fills up the large ditches between people's houses, and leaves the houses dry.

Suppose I implement better, but imperfect, security. It now costs an attacker $6 million, in salaries, paying for exploits, whatever, to hack my system. They still can only get $5 million in ransom. The attack isn't worth doing anymore, so they find a different business.