Because it seems that, to exist in society, is to give up some form of privacy by dint of existing in it.
You cannot stop yourself from being observed by other people, if they can see you. That’s just basic reality.
To be completely private, you would have to live in the woods and not interact with anyone or speak with anyone.
Is it defeatist to be realistic about the limitations of the idea of privacy?
As someone who has spent a lot of time seeking internet privacy, I’ve learned that more often than not I’m making myself more conspicuous. That doesn’t mean I’m going to give up on privacy, but it does mean that I’m going to consider its limitations.
EDIT: I’m reminded of an interview with Mark Hossler from Negativland. The interview is long gone from the internet (it was on an obscure website pre-youtube) but the center of it always stuck with me.
“If you really want full control of your art, don’t show it to anybody, keep it in your home.” His argument was Richard Dawkins’ argument for memes. The human mind functions by copying and mimicking. When someone else has viewed your artwork, they’ve already created an internal image of it in their memory. That memory is inconsistent with reality, but if they have a good memory, they can recreate it relatively easily (if they have similar artistic skills). You can’t really stop that kind of copying from happening, so the only way to fight it and keep “complete control” is to not share it at all.
Similarly, the only way to have complete control over your privacy is by not interacting with anyone at all.