> need to migrate everything from their walled garden (at great cost)

It's not just about migrating the phone, if you own an Apple Watch, AirPods, one of their laptops, their online services, etc. all that stuff works best within the Apple ecosystem. If you move they don't work as well (if at all) and you may need to replace them. If you are deeply bought in to Apple products, it really isn't that easy to move.