Originally Posted by
gpobernardo Facebook and Twitter integration were not really "lost", the process was just modified. Instead of being able to integrate your contacts from Settings > email+accounts, integration can now be done through the respective official Facebook and Twitter apps.
Well, its a bit more that that. I can't post directly to someone's FB page nor comment on something without having FB installed and launching the app.
One of the main selling points of WP was that all of that was baked into to OS. Now its not. The Messenger and FB apps drain battery, are slow, and add another layer of complexity that wasn't there before.