because this is a tool for doing work? Nobody (or very few) HN people are going to want to do BI with their facebook accounts, if we even have FB accounts.
Outlook is bigger than Google for corporate email. I would suggest adding that (or better yet, listen to the other feedback and allow a standard email login flow).
My boss would not be happy if I had to use a Facebook account on my work machine.
And who evaluates BI tools in their free time?