1. The penalty of social ostracism due to the network effect. This is a severe punishment to most humans - particularly in today's socially disconnected world. Without these apps, a large # of people would not have any contact with much of their social circle - including family.
2. Learned helplessness. I think that many people have just given up. Even if they knew how to fight for their privacy, they see time and time again that money always wins.
This is old thinking. In the 90s and 00s it was miraculous to trade in a little privacy for some awesome free service on the internet. Google, Facebook and others became huge, and everyone has been influenced / manipulated by them and people are getting tired of having a family dinner conversation next to their smart speaker and seeing ads for six weeks for Depends diapers because someone told a bad joke at the dinner table.
Take all the paranoia and “muh privacy” around contact tracing or the European Green Pass: It’s as anonymous as it can be, yet millions of people argue against them across the political chasms that separate them. So yes: unless it becomes a divisive topic (which would be undesirable), this CSAM scanning will go away with the news cycle.
About your comment on celebrities’ “sex-tapes”. I guess it takes a certain kind of extroversion and (positive) narcissism to be one, and they’re expected to be gossiped about or to show their bodies in movies or photos so I don’t think those victims blinked that much - some like P. Hilton probably manufactured some porn to ride the wave. On the other hand, revenge porn did drive ordinary people to suicide because in this case the victims weren’t prepared or expected to let the public to see that.
Who knows how much it will matter in the end? But it is hard to argue it doesn't matter.
Plenty of people believe that the Facebook and Instagram apps are recording audio 24/7 and target you ads based on the speech the apps hear. That doesn't stop people from using the apps.
A few years ago some of the most famous people in their world had their iClouds accounts hacked and had their naked photos leaked. That is a lot of people's worst fear. People literally commit suicide over this sort of thing. It didn't hurt the iPhone's market share.
People largely don't care.