Another reason to vote again on the same content is that it may be updated, expanded or otherwise edited. A good part of the the idea of allowing edits forever is to encourage maintaining/improving existing and reducing the need to repost it.
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posts wouldn't be considered "active" unless they received enough votes to "activate" the post itself
That isn't possible. The decision to "activate" a post would be a consensus decision so the voting that led to that happening would have to be part of the consensus state.