He has the "Pwned Password" search to allow you to narrow it down and he has a really good article that he links to explaining why despite its inconvenience.

If I was him I'd do the same. HIBP is a side project of his and I wouldn't be able to sleep at night knowing I have the responsibility of securing billions of email & password combinations.

At the risk of the breach of those accounts adding fuel to the credential stuffing fire and reducing his overall credibility when providing security advice which is his primary occupation.

Too risky.