Well it's hard to say how much of the growth is growth in detection/reporting versus growth in underlying crime, but it's worth noting that each transmission of CSAM is considered a separate crime. I.e. even if actual sexual assault remains steady, the nature of the internet (virality and community creation) sort of pushes CSAM transmission upwards. The internet is designed to spread content that people want, CSAM is sadly just that.
What do you mean by CSAM proliferating? Do you have evidence already that CSAM's image database is being used in a much wider scope than Apple is claiming?