I’ve got a longer response in the works, but I thought this snippet from Chris Messina’s post about OpenID Connect was particularly insightful (and not even from the main point of this post):
That is, because OpenID users share less information with third parties, they are perceived as being “less valuable” than email-based registrants or users that connect to their Facebook or Twitter accounts.
So while it might seem like an inconvenience to custom-tailor your personal privacy settings on Facebook, the liberal defaults are meant to make Facebook users’ accounts more valuable to relying parties than other, more privacy-preserving account configurations.