They ARE Scanning your photos on device. From the Apple FAQ:
Apple’s method of detecting known CSAM is designed with user privacy in mind. Instead of scanning images in the cloud, the system performs on-device matching using a database of known CSAM image hashes provided by NCMEC and other child safety organizations. Apple further transforms this database into an unreadable set of hashes that is securely stored on users’ devices.
Use whatever tech babble you want, "On-Device Matching" IS Scanning. Apple looks through your photos, finds naughty things, and tells the cops. All without warrant.