Mr. Daniels, who previously ran Facebook’s business development team and had other roles, was appointed head of WhatsApp last May. He became upset at some of the choices that were being made to connect the apps, said people familiar with his thinking. He was also concerned that Mr. Zuckerberg’s plan would harm the success of WhatsApp, which is particularly popular outside the United States.
Because of those changes, Mr. Daniels handed in his resignation months ago, said two of the people, though the decision did not become public until Thursday.
Mr. Cox has also been frustrated with Mr. Zuckerberg’s decisions in recent months, some of the people said. Less than a year ago, Mr. Cox shifted into one of the most powerful positions at Facebook as chief product officer, responsible for overseeing Instagram, WhatsApp, Messenger and Facebook itself.
Almost immediately, Mr. Cox ran into difficulties, the people said. Employees said he disagreed with some of Mr. Zuckerberg’s product ideas and changes, including the “unified messaging” project intended to connect the apps.
But Mr. Zuckerberg had already made his decision. Mr. Cox informed Facebook of his decision to leave on Monday, according to a company filing.
“For over a decade, I’ve been sharing the same message that Mark and I have always believed: Social media’s history is not yet written, and its effects are not neutral,” Mr. Cox said in his post. “As its builders we must endeavor to understand its impact — all the good, and all the bad — and take up the daily work of bending it towards the positive, and towards the good.”
Mr. Zuckerberg has promoted others to take the place of those who have left. Adam Mosseri, a longtime Facebook employee, was promoted to head of Instagram last year. On Thursday, Mr. Zuckerberg said Will Cathcart, another Facebook employee, would run WhatsApp, and Fidji Simo would lead Facebook’s main app.