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I think much of it is just individual players trying to do too much on a bad offensive team. Players get in a mode where they're trying to hit XBHs when its not their game and destroy their overall offensive value.
I don't neccesarilly think that you need a big bat in the lineup to legitimize it (it could be well-balanced lineup), but the players need to have confidence in the offense or sometimes they never recover from slumps.