The large majority of duplicate closures are done by a consensus of three people, and the large majority of the rest are done by people who have a badge indicating expertise with the subject matter in addition to the close-vote privilege. It is not done by "the mod"; there have historically been about a couple dozen moderators for a couple dozen million user accounts.

Generally, the people doing this are familiar with the material. Fast closures are motivated by an unconscious "ugh, not THIS question again". And the kinds of things that get asked over and over usually don't change very much.

There's a particular type of question asker who likes to say "what's the way to do this in [current year]?" as if to imply that it should be something different from before. But it very often isn't. And indeed, developers complain when languages/libraries/ecosystems change too quickly, which makes language designers/library authors more conservative about those changes.