the social network - Why is Adam D'Angelo's character not in the movie?

Adam D'Angelo met Facebook co-founder Mark Zuckerberg while the two were still teenagers attending "uber" preppy prep school, Phillips Exeter Academy. Initially, D'Angelo worked on the first "app" for Facebook called Wirehog, a peer-to-peer file sharing program. He later went on to become Chief Technology Officer where he led the Platform Development and Data teams, and oversaw new product design and architecture. D'Angelo maintained the CTO position for two years before leaving in June 2009 to co-found Quora, an online database of information organized by questions and answers created by users.

So given that he's an important person in the history of Facebook, why wasn't he present in the movie The Social Network.