What am I missing?
http://files.arcfn.com/doc/variables.html#defhook
You're right that it isn't used in the codebase, but perhaps it's used at the REPL or something like that.
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Lol... I remember asking the same thing.
news.arc does not dynamically add and remove hooks, so the hook abstraction seems redundant. And the defhook macro is unused.
My conclusion is that hooks were something to experiment with originally, and later back away from.