If they stored terabytes of any data on a cloud based system, wouldn't they run into the same issues? I think I sort of get where OP is coming from, but I can't say I ran into the same issues.

Ive personally used the export / archive features of iCloud when i went from iOS to android. the longest part was waiting for the pics / vids to download from icloud and upload to google drive.

I even exported stuff out of google's ecosystem and back into iCloud when I moved back. This was a month or two ago.

I know many many years ago I had issues with iCloud, but that was before they fixed / improved their web interface (and everything else).