Either way, as it stands now it doesn’t cost the company anything to have the devices shredded. Without activation locks it will, either by forgoing the premium paid by the recyclers or by having to pay a shredder to do it for them.

It’s a power difference. Activation locks give companies more power to control what happens to devices after they’ve left their custody. It also makes it more likely for devices to get shredded because companies need to affirmatively consent to the devices being resold after leaving their custody. This benefits Apple by taking used devices off the market.

This affirmative consent element is also quite powerful in the consumer space for the same reason that opt-out organ donation is so successful: people generally prefer defaults and shy away from making extra decisions that complicate their lives. This means people are much more likely to trade in their old phones to Apple (who either shred or sell as refurbished) instead of selling on the open market.