I guess because people are reminded weekly to resubscribe or buy subscriptions as gifts.

I dunno if it applies to me since I would habitually forget to resubscribe until they sent me the YOUR LAST ISSUE wrapping like an invasive Santa Claus.

Opportunity cost of lost subscriptions. A certain percentage of those inserts will convert to new subscriptions, even if the person receiving the insert was already a subscriber.

Some of those inserts were invitations to subscribe to the Economist.