People will use Facebook if the majority of their friends use it. For many years, WhatsApp didn’t use end-to-end encryption, but people used it because it got to a tipping point where so many people were on it, that using another texting solution (eg Messenger or iMessage) didn’t make sense.
Also, people will be assessing the value they get from Facebook vs. the cost (in terms of user profiling).
Let’s say that you’re happy for FB to use the information you post there to create an accurate customer profile, and then sell that information to advertisers - it’s the same deal that you sign with ITV (we give you content, but we will support ourselves with advertising).
Facebook is a fundamentally useful free communications tool. That’s why billions of people use it. It’s why it will continue to be the world’s leading social media platform, until the early adopters decide thatit can be replaced (cough cough...myspace...cough cough).