Being able to install a new os is orthogonal to owning a device. It's an additional feature that most users won't use.

Being able to install a new OS is not an 'additional feature'. It's the downgrade of a capability that's inherent to the device. It's the same as making a carseat heating a subscriptions service. Whether the users use it or not is entirely irrelevant.

the "ownership" framing is because bootloader locks allow vendors to unilaterally make decisions about how your device operates after you purchase the device.