I think this is because Facebook, as a social media has been built for you to connect with your peers whereas Twitter has been used as a broadcasting platform to allow you to connect with people that you do not have direct connection with. The fact that one can have as much followers on Twitter makes it a more efficient platform especially in communicating with your audiences. Remember that the sharing feature or Retweet originated on Twitter with this very concept of sharing information, with the added feature of trending topics to keep people updated of the current and most-talked about issues.