To prevent users from collecting up "their friends" info to import into Google+
"...The activities surrounding the export tool spotlights the value of the data contained in social networks. Google believes people should be able to extract information about their contacts and provides tools to let people do so. Facebook, the incumbent power in social networking, provides only a tool to let people extract what they themselves have put into the network. The friend list it provides is a series of names in plain text--no contact information, and not even a link to their Facebook pages to help distinguish John Smith No. 1 from John Smith No. 2..."