It's a question I've asked myself. The writer here has some pretty good insight.
https://www.yahoo.com/tech/m/fe40df39-7c2b-3439-8975-eda2fe1480d1/ss_want-to-know-julian.html
https://www.yahoo.com/tech/m/fe40df39-7c2b-3439-8975-eda2fe1480d1/ss_want-to-know-julian.html