This site used to play a different role. It used to be called Meta Stack Overflow, and used to be the Meta site for Stack Overflow and the whole network. It has since been renamed to Meta Stack Exchange and a separate new Meta Stack Overflow was added.
As such, the FAQ here has undergone a few changes as posts specific to Stack Overflow have either been migrated or just outright deleted here. A few hours ago, Shog migrated What do the colors on Stack Overflow mean?, for example. It clearly applies to Stack Overflow only, no to all Stack Exchange sites.
More generally speaking, the Stack Exchange stack is not static. Things change. If a feature were to ever go away, then at some point a dedicated FAQ for that feature would have to go away too.
In the past usercards on questions included an accept rate for example; the percentage of questions asked by the user where they had marked an answer as accepted. This led to badgering and bullying about a number that never was meant to mean anything. This feature was removed and any mention of it in FAQs should be long gone with it now.
Most of all, the FAQ is community curated. People that care a lot about the Stack Exchange stack maintain it, through editing and creating new pages. See the procedure at the bottom of the central FAQ page for how this works.