You answered your own question: > What I don't understand is why Quora was/is loved by people like the Facebook team ... The fact that they require you to log

You answered your own question: > What I don't understand is why Quora was/is loved by people like the Facebook team ... The fact that they require you to log in __via a social account__ Quora "furthers" facebook by requiring a facebook account, so naturally the facebook team will "love" it. It furthers their (facebook's) business interests.