The official reason they dropped it is because there were security concerns. The more likely reason was the massive outcry that occurs when Apple does these questionable things. Crickets when it's Google.

The feature was re-added as a child safety feature called "Comminication Saftey" that is optional on a child accounts that will automatically block nudity sent to children.

They were not “suspected” they had to be matches to actual CSAM.

And after that a reduced quality copy was shown to an actual human, not an AI like in Googles case.

So the false positive would slightly inconvenience a human checker for 15 seconds, not get you Swatted or your account closed