Why? Is it complicated simply because privacy itself is complicated? Well, it's certainly true that privacy isn't as simple and clear cut as some might imagine, but does that really mean that privacy policies, and privacy options need to be so complex as to require a law degree to even begin to understand? It's hard to justify - and for companies that demonstrate immense creativity when it comes to designing new products and services, and excellent ways to make those products and services simple to use and easy to understand, it does seem quite surprising that they can't make their privacy policies easy to understand and their privacy options simple to use. They have the experience and the expertise to find a way - if they really want to.
The second possible reason is far more shady - maybe they want to make privacy complicated because they don't want people to know what they do and what the implications are? If an ordinary user has to wade through a document the size of the US constitution, and spend their time choosing between 170 options and 50 settings, the chances are that they simply won't bother. And if they don't bother, and leave the settings on what Facebook choose as the defaults, then everything's much happier, at least for Facebook.
I wouldn't like to suggest that the second is true - the first is far more likely. However, if the second does have an element of truth to it, we might start to see that over the next year or two. Public interest in privacy appears to be growing - the question is how companies like Facebook respond to it. If things change, and change quickly, that would tell us a lot. If they don't, and if there is more prevarication and less action, that would tell us something else entirely.