They basically did. If you turn on Advanced Data Protection, you get all of the encryption benefits, sans scanning. The interesting thing is that if you turn on ADP though, binary file hashes are unencrypted on iCloud, which would theoretically allow someone to ask for those hashes in a legal request. But it's obviously not as useful for CSAM detection, as, say, PhotoDNA hashes. See: https://support.apple.com/en-us/HT202303
