I think you have to be aware of what is happening, before you can say that nothing criminal happens. This is where scanning steps in. You can’t turn blind eye.
There is a big jump from reporting criminal activity if you happen to see it, to actively searching it out. It is the jump from police arresting you if they see you smoking a joint to police searching your rooms to make sure you don’t have any cannabis in there.
I read the law and you are correct, there is explicitly mentioned that provider is not required to enforce seeking of CSAM evidence.
However, they might be required to comply the demands of NCMEC if they ask to stop redistribution of certain visual depictions by providing hashes. This is were scanning steps in.