#Wikimedia contributors contribute in more then one language and on more then one project. The approach to our projects however is isolationist. Every project is separate and there is not much that helps the cooperation between projects. There is no way that you can reliably get the attention of a wikimedian.
At this stage I have 491 users on 491 projects consequently I have to state 491 times that I am male, what my time zone is, my preferences for editing ... There are 491 user pages for me and having something sensible on them, something that is of interest is just too much effort.
Now consider that an e-mail is to be send to all the localisers who localise MediaWiki from English into Dutch ... Or how about an invitation to all the people who speak Lingala to participate in an interview about their issues with editing Wikipedia.
At this time we cannot because our perspective is very much the perspective of the single project. We just found out that the majority of us is multilingual and edits in multiple languages. The social reality is that our editors can be found everywhere. We do not make it easy for them to coordinate things.
We need social network functionality because we need the social coherence that goes with a community that is all over the place.