1. To make it clear what is your work, and what is building on someone else's.

2. If the paper turns out to be important, people will bother.

3. There's checking for cursory correctness, and there's forensic torture.

building on imaginary someone else? That's exactly the same as lying. Is a review not about verifying that the paper and even data is correct? I get reviewers can make mistakes, but this seems like defending intentional mistakes.

I mean, in college I have had to review papers, and so took peer review lectures, and nowhere in there was it ever stated that citations are not the reviewer's job. In fact, citation verification was one to the most important parts of the lectures, as in, how to find original sources (when authoring), and how to verify them (when reviewing).

When did peer review get redefined?

I'm not defending dishonesty, I'm saying that's what citations do when they are used by honest people.