Its probably because Apple would be legally required to hand shit over snd Apple does a number of things like when you sign in the normal way it activates iCloud and backups everything and makes everything available to icloud.

Everything used to be cleartext to apple before advanced protection (even tho thats more like a bulletproof transparent glass window, rather than black box) so if they had to hand user accounts over, they got everything. Its probably still that way there

Also, by default it backed up to iCloud (Backups) which contained iMessage keys as well so they could pretty much get access to everything). I imagine russia forces Apple to escrow all e cryption keys like on Mac and whatever else