Apple services are realtime keys to:
- activation: wiping an iOS/iPadOS/visionOS device, or reinstalling a mac after a full disk wipe
- apns: push notifications, used for realtime notifications for all apps on iOS/iPadOS, even things like Signal that do not use Apple's messaging infrastructure
- imessage: enough said
- boot ticket signing: required for any mac to do an OS update (it's serialized to the CPU's ECID)
any one of these going down for any significant period of time is going to cause widespread global economic disruption.