The latest episode of The Daily podcast [0] from The New York Times said that Apple executives were told by members of Congress at a hearing that if they didn't do something about CSAM on their platform the federal government would force them through legislation. And it's not a completely idle threat; just look at the proposed EARN-IT Act of 2020 [1], which would pretty much outlaw end-to-end encrypted services without a law enforcement backdoor.
[0] https://www.nytimes.com/2021/08/20/podcasts/the-daily/apple-...