A better analogy is a storage locker. AFAIK police need a warrant to search "your" storage locker even though it's on someone else's property. I don't see why data in the cloud should be any different. Pre-emptively scanning everyone's data is equivalent to officers rummaging through all the storage lockers in a facility "just in case" they find something illegal.

It’s a bit more like requiring you to submit to a weapons pat down before you go to your locker I think.