My take: this was done to pull consumers back into the cycle of upgrading to every new release. iPhones already do so much more than most people need. With the RAM price hikes, even though there was an influx of sales (according to a store rep) initially, I think Apple was expected a significant decline; people just choosing to stick with their current device to avoid paying the premium.
Leasing not only allows Apple to keep "selling" people new devices, it will also mostly like accelerate the second-hand sales and resource recycling arms of the business. Consumers will be more willing to upgrade sooner and stay in perpetual payments vs having to buy out the device at lease end - and Apple gets back newer devices where the recycled tech is arguably more valuable.
