Anyone who joined, or stayed at Facebook, in the last say 5 years, 100% knew about it and was OK with it. They’re probably laughing at everyone else taking so long to figure it out!
I had my own experience, once, leaving a company due to ethical concerns: it took me a year and a half to finally follow through and quit. I had coworkers who felt the same who stayed on for years.
No doubt the thought that occurs to many FB employees when they read these articles is "I need to gather my resolve and get the hell out of here!"