There is a fairly large caveat to this and it happens to also deal with children.
18 U.S. Code ยง 2258A - Reporting requirements of providers
In short, it requires ESPs to report incidents of child exploitation that they become aware of to the National Center for Missing & Exploited Children.
According to NCMEC's published data there were over 20 million reports in 2020. The latest breakdown by ESP I could find was from 2019, which shows facebook making 15 million reports.