How about security through obscurity, to some extent? An IPv6 address isn’t a needle in a haystack, it’s a needle floating somewhere in the solar system. I think I have a quadrillion addresses assigned to me?

340,282,366,920,938,463,463,374,607,431,768,211,456 unique IP addresses is a staggering amount to scan, no matter what horsepower you have to deploy.