I thought the primary reason was privacy: <a href="https:&#x2F;&#x2F;m.facebook.com&#x2F;notes&#x2F;facebook-engineering&#x2F;protecting-privacy-with-referrers&#x2F;392382738919&#x2F;" rel="nofollow">https:&#x2F;&#x2F;m.facebook.com&#x2F;notes&#x2F;facebook-engineering&#x2F;protecting...</a>