Back in the physical swipe days, the embossing of the card and carbon paper made an imprint. The imprint was not just the card number, but demonstration that the card was actually there when the imprint happened.
"Track 2" data is similar; I dunno what it contains, but provides similar evidence that the actual card was actually used.
Expiry date help for phone or internet transactions, as does the CCV2 codes; just more evidence that someone has the card in hand.
Generally, the theory was that it is hard/impossible to copy two of these at the same time. Signature and CC # embossing are on the opposite side of the card. CCV2 # and CC#, opposite sides (for most cards), etc.
Obviously, as time has moved on, the effort/gain ratio of each of these has been overcome, and thus the introduction of more things.
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