How Facebook CEO Mark Zuckerberg earned $296 million in one month

Facebook CEO Mark Zuckerberg is the world’s fifth richest man. In the month of August, according to a report by CNBC, Zuckerberg sold 1.6 million shares of Facebook which netted him close to $296 million.
The report further states that Zuckerberg hadn’t sold any shares since April. However, including the sale of shares in August, the Facebook CEO has now sold 2.9 million shares in 2019. These shares are said to have been worth more than $526 million.
There has been no official reason given on why Zuckerberg has been on share selling spree. In the past, however, when Zuckerberg had sold a bulk of shares, he had funded Chan Zuckerberg Foundation, a philanthropic organisation he runs with his wife.