Apple and Google had no choice but to comply with the National Security Letters demanding access to user's push notification data.
They also can't refuse to comply with warrants demanding any such unencrypted data that is stored on their servers.
That's not the same thing as adding a back door to allow access to encrypted user data that is stored on the user's device.
It's also different than storing encrypted user data on your server, when you have purposefully designed a system where you don't have access to the user's encryption key.
Encrypted user data backup is the feature that Apple disabled access to in the UK rather than comply with the order to insert a back door in the OS.