It was either the Economist or FT that did a cost/benefit analysis of removing those inserts for their already-subscribed customers copies, and found that it would cost more in lost new subscriptions to remove them.
How does that make sense?
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.
Force the publishers and advertisers to pay the postage for them with the idea of making it less profitable to include them with the magazines in the first place.
Years later, on the internet, I remember seeing some article about people doing this, and they had pictures of things like business-reply envelopes attached to bricks, which the USPS had received. IIRC, they said that the USPS didn't actually send these or charge the business for them, unfortunately.
So stick with just dropping them in the mail as-is, to make sure the business gets charged for it.
They had been told that each application cost a dollar to have mailed and processed.
I was a child so I never cared enough to ask about the details of the dispute and I don't know how long they did this, only that they did.