Managers are rewarded for focusing on tactical efficiencies. Their jobs are to get the people working with and for them to deliver value to the internal and/or external customers. Done correctly, it's an operational focus. The tighter the organization becomes, the more promotions until the leader gets within sight of the CIO job. Dead End. Being even more blunt, if you know of a CIO that was promoted from within you will usually find a marginalized IT organization that is not strategic and not invited to the table with the executives.
CIOs focus energy on the business strategy, not on operations. The board and executive peers are the chess pieces that when influenced, align the organization to that strategy. When done correctly, the CIO fights for the future. His or her time is prioritizing future over current as much as possible. Growing the leaders below to handle the operations allows strategic work for the CIO. Good CIOs grow their direct reports to protect the CIO's strategic time by 'handling it'. Good CIOs live in the future; what is happening today on whatever project is over to them. There are bigger fish to fry.