As an aside, I thought I read a year or so ago that this is all temporary as Apple is building out its own server farms. Aren't some of their services already on Apple servers (e.g. the App Store, videos, music, etc.?)
Apple run their own substantial CDN for servicing things like Apple Music, software updates and App Store downloads. A redditor who claimed to be a Google Engineer (yes yes, make of that what you will) reckoned they're more or less just using S3 and Google Cloud as dumb storage for encrypted blobs. This gives them a modicum of diversity/redundancy and allows them to play off suppliers for $/TB whilst also offering superior performance in regions where AWS/Google have Data Centres but Apple don't (yet).
Unless anyone has cracked AES256 (or Apple foul up spectacularly and lose everyone's private keys), it's not something we should be terribly concerned about.