The reason that trust is important could be to do with verifying breaches.

In some of his articles discussing various breaches, he mentions reaching out to selected (potential) victims to verify some of the details.

Doing that does require a fair amount of trust by various victims of the people asking to verify.

If I was randomly contacted to verify some details in a breach, I'd be skeptical it was a phishing scheme.

If I was randomly contacted by Troy Hunt / HIBP - then I'd look at it much more seriously.