Why is my plastic credit card and activation code sent separately?

Capital one recently sent my plastic credit card by paper mail and it’s activation code by a separate paper mail. What security problem does this mitigate? If a rogue element has access to my mail box or home, they will have both the plastic card as well as the activation code. The only thing I can think of is that they are preventing rogue elements on their side from having access to the two information at the same time? Or is it something else?