I agree, and I work on a team with impressively thorough review habits. The obvious reason is that tests allow reviewers to focus on more substantive questions

I agree, and I work on a team with impressively thorough review habits. The obvious reason is that tests allow reviewers to focus on more substantive questions than what the code behavior is (eg “is this the desired behavior?”). A less obvious reason, but more compelling to me, is that code which hasn’t changed is very unlikely to be reviewed in the context of changes under review, even if the unchanged code should have changed.