It is not a technicality, it is scanning, and the answer is yes. My device, my data, Apple's Servers, their data. Since the goal is to keep CSAM off of Apple servers, it's best to scan there.
That's just one goal.
Other (side) goals might be:
- Reduce the number of people using Apple products to store and spread CP
- Show lawmakers and others that Apple is doing something to combat this
- Reduce the economic incentives for selling and buying CP by making it more difficult to perform such transactions (if you buy CP you have to store it somewhere)
- Being able to provide end-to-end encryption for more data in iCloud in the future