According to an in-depth Vanity Fair article chronicling the departure of Jason West and Vince Zampella from Activision and the lawsuit that followed, the duo who helped make Call of Duty a household name were not getting along at their new studio Respawn Entertainment. Last month West left the company to deal with "family issues," but those issues may have had more to do with his work family than his home life.
An anonymous source speaking to the magazine said that West's behavior was erratic while the company was working on Titanfall, which made Zampella angry. During the latter development of Titanfall, West was reportedly not coming into the office at all, according to the source.
"Vince felt that Jason was sabotaging the company," said the source.
"It's hard to work with one person for 15 years," Zampella told Vanity when asked about West's departure.
Ultimately this led to Zampella taking over the studio and the game. How the duo worked out a deal that allowed West to be compensated for his part in Respawn and its new game is unknown. Given the protracted lawsuit with Activision it is doubtful that West simply walked away without any sort of compensation...
You can read the whole account here.