Because the complaints she is making and that people find most offensive regarding Facebook are not its data collection. I know that is an unpopular opinion here, but many people don't care about data collection because they don't see how that negatively impacts their lives.
There are sizable populations of people that think the Facebook apps record all audio they hear and serve ads based off what you say in front of your phone. That doesn't stop those same people from using those apps.
The primary problem that the general population has with Facebook is how their algorithms manipulate in the name of profit both at an individual level (e.g. making people feel bad about their lives) and at the societal level (e.g. increasing political division or censoring political speech). Those are the topics on which Haugen is whistleblowing.
The reason this is a more effective line of attack against Facebook is because the negative results are inherently obvious. How does Facebook spying on us have a tangible impact on my life? For the most part it doesn't. Who cares how that data impacts what ads they show you? The impact is more philosophical for most people. How does Facebook manipulating us to make us angry and/or sad have an impact on my life? Well, clearly many of us are angry and/or sad now. Everyone can recognize that is bad.