I think there are two main reasons why Zhang Yong can become the CEO of Alibaba Group:

The first is his outstanding performance. Although Zhang Yong was the CFO of Alibaba Group at the beginning, it is unlikely that a person who works in finance will become the CEO or the company's executor. However, before Zhang Yong was elected CEO in 2015, he led Taobao's sales and user numbers to grow significantly year-on-year, especially the performance of several Double 11 events, with sales constantly setting new highs and bringing huge benefits to the group. With this outstanding performance, Jack Ma also recognized his ability and gave Zhang Yong the CEO position.

The second reason is that Jack Ma wanted to find a candidate for his retirement, and Zhang Yong, who performed well, became the only choice to take over Jack Ma's position.