Because they're not CSAM?
People don't seem to grasp what kind of images end up in the CSAM databases. They are most definitely not "leaked celebrity nude selfie" level stuff.
Think of the most vile sexual thing you could do to a child and then times that by two and halve the child's age in your mind. That's the shit that gets in there.
It's not something even 4chan weebaboos share. It's stuff that makes Liveleak regulars go "ewwwww, gross".