Why would a web site hide the log out button?
I have recently observed many sites that do not have a log out button. Either it's not there or hidden somewhere so that you have to find it. Why do you think this has been done? Does it apply to every category of site - for example a social networking site versus a banking site?
The original poster is talking about how many site are hiding the logout link. Facebook makes you open the account menu to see the logout link.
My guess is that there's really no need to log out of your account these days. Public computers are not used as much anymore, so there's no need to protect your privacy. Everyone owns their own personal laptop or computer. We even have personal cell phones with browsers. Only you have access to your personal devices, so why go through the hassle of logging out every session and typing in your long ass email / password whenever you come back? Web designers realized this and they hide rarely used features to make room for showcasing more heavily used features.
I can think of plenty of reasons I'd want to log out of Facebook (not that it would stop them tracking me...)
Actually, staying logged in seriously increased the changes of a CSRF / confused deputy attack where you might think you're taking an action on a site but really you're clicking an action on Facebook which is in a transparent frame above what you see, for example