Why Rib Cast On Needs Double Knitting

Why do we have to do double knitting instead of knitting rib stitch immediately after hanging the yarn on the needle?

The structure of Stockinette is flat.
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Ribbing structures have three-dimensional depth.
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At the stage of hanging the yarn on the needle, there are still only two rows of knitting.
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Double knitting produces a third row of knitting.
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Three rows of knitting can create a three-dimensional structure with depth.
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