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.
By encouraging users to stay logged in, service providers like Google and Facebook can not only make the login experience less of a hassle, but (perhaps far less innocently) gather browsing data and habits on their users (even when they're not using the service) to enhance advertising intelligence.
And that's something that makes me wary.
One reason to hide it is for caching.
For example on your home page, if you're logged out show
login button. If logged in show
logout button. This kills the cache.
However, if there's a menu that says
my account, and its contents are loaded dynamically, you can cache the rest of the page. This increases performance.
It's because of sub-services they offer. For example, in order to reply to discussions on some third party sites, you'll need to be logged into Facebook. Or, in order to leave a YouTube comment, you'll need to be logged into your Google account.
If the user logged out each time they navigated away from the core service, they'd have to log back in each time they wanted to do something else that relied on the service.
Also, when you're logged into a service like Google or Facebook, you're bound to their TOS. They are able to track certain activities. This is to their benefit.
From a user perspective, logging in is a hassle.
why? because users need to remember and input their login info and sometimes tend to forget their login details, then they need to go thru the process of password reset or recovery which is a pain.
proof of this. the widespread use of the integrated login with facebook and google plus button. let's face it. humans are too lazy to logout and login again.
Personally i hate it when a website or app logs me out for some reason of when i reset my browser cache.