Because CSAM isn’t something you should be giving ‘warnings’ about.
If you’re drawing something that could be construed as CSAM then you need to have a word with yourself but we’re all adult enough to know that some people just like testing where the line is, or knitting where it is and remaining just shy of it then feign ignorance.

It did because there was a noticeable quality bump after third party apps were cut off so while it didn’t cause most users to leave, it made a substantiative jump further down the enshittification path that will eventually alienate everyone.