When a superdense, concentrated mass forms a black hole, the laws of physics around it change, giving rise to an eldritch zone where the normal rules don't apply. When corporations form a concentrated industry, the laws of economics likewise change.
Take copyright: when I was a baby writer, there were dozens of comparably sized New York publishers. The writers who mentored me could shop their rights around to lots of houses, which enabled them to subdivide those rights.
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